The Big Bad has just learned that a child that can defeat him has been or soon will be born. The obvious solution to this problem is to Screw Destiny. Nip this danger in the bud and kill the Infant Hero before he can become any kind of threat. This is the stage where the problems crop up. Either the Big Bad has no idea who this child actually is, or other characters also aware of this destiny have taken the initiative to hide and protect the child before the Big Bad can actually reach him. Or the would-be killer thinks they've done the deed, but unbeknownst to them, some force or benevolent person intervenes and child is actually Not Quite Dead. Whatever the mechanism, the upshot is that You Can't Fight Fate.
Often the only thing to do in cases where they can't identify the child is to attempt to track down the newborn hero, baby-by-baby if necessary. The Big Bad will investigate or, if impatient, simply kill any child in the proper age range to attempt to secure his safety — this may result in a Childless Dystopia if he's thorough enough. Inevitably, it never works, and if innocent childrenare killed, the resultant crossing of the Moral Event Horizon makes clear just how bad the villain is - and of course karmicallyseals their fate. Worse yet, this act often directly backfires, giving the hunted newborn a reason beyond mere prophecy to go after the Big Bad after he's grown up enough to take him on; see Self-Fulfilling Prophecy.
This being a form of Villain Ball, it almost never occurs to anyone that a wiser thought might be to try to find and raise the child himself. Though you might occasionally see it among the more Genre Savvy villains, who take the view that the kid might love him too much to finish him or, in the worst case scenario, will be close at hand if he doesHeel-Face Turn. This often doesn't work either, though, and is irrelevant if the prophecy is that the child will defeat him.
Sister Trope to Genocide Backfire, with which it can and does overlap. The primary difference is that this trope is specific to a Big Bad trying to find a newborn Hero before they can be a threat. No more or less. Genocide need not be a part of the method. The main factor for whether or not such a situation is this trope is if the genocide is merely a means to an end (Kill Tribe A to prevent the rise of Child B) or an end in itself (Kill Tribe A to stop any rising, period).
Also compare Offing the Offspring for those occasions when the child is the son or daughter of the Big Bad. See also Infant Immortality, which is, in writing terms, one of the primary reasons this rarely succeeds.
Not to be confused with Nice Job Breaking It, Hero. However, it can be related to Nice Job Fixing It, Villain.
An interesting variant in Elfen Lied — the antagonists actively seek out and imprison diclonii as they're born. Their primary approach is to visit hospitals daily and inspect the nurseries, looking for horns. If one is found, they then make every effort to persuade the unlucky parents into giving up the infant, and if that fails, they take it by force with the assistance of hospital security. Then they go on to enslave and torture the children and, down the line, are surprised when they turn out twisted and angry.
Scrapped Princess. Legends speak of a royal princess who will destroy the world. When she is born, the Church of Mauser throws her off a cliff. The queen arranges for someone to catch her.
The main villain of Mugen Densetsu Takamagahara Dream Saga actually does think of raising the kid himself. He just picked up all the kids it could have been and killed them when they proved not to be the one.
This happens in some versions of Osamu Tezuka's Dororo. While in the original, Hyakkimaru's father simply sold his body parts to the 48 Mazins because he wanted power, most later versions had the Mazins offering him the deal because they knew his son was destined to defeat them. The fact that Hyakki is The Messiah does go a long way toward explaining how he can survive with most of his vital organs missing...
Mahou Sensei Negima! has some traits of this, since it has now been explicitly stated that the demon attack on Negi's village targeted him. He was one of the twonote three if you count Anya, who was studying abroad at the time survivors and is really pissed.
Well, in Negi's case it was more of Sins of Our Fathers... er... Sins of Our Mothers. Since the ones responsible were going after Negi because they couldn't go after his mother, in revenge for crimes... they framed her for.
Saint Seiya also has an example of this, though the infant is well identified. Renegade Gemini Saint Saga murdered the rightful ruler of Sanctuary, and tried to assassinate Athena's reincarnation which was still an infant. She was saved in the nick of time thanks to the sacrifice of Sagittarius Aiolos, Saga somewhat convinced himself that he had succeeded in getting rid of her, and had his comeuppance and a lot of cold sweating when he found out she was well alive, and had founded her own guard of Saints.
The Storm Riders has a bit of a variation of this. Lord Conquer was given a prophecy for the first half of his life, which led to him slaughtering the families of the two heroes and adopting them to secure his reign, but isn't given the second part, in which they will bring him down, until they're grown. However, his attempt to stop this from happening cause it anyway.
The "Messiah compleX" arc of X-Men was about numerous different factions (for their own reasons) trying to find a new-born baby who happens to be the first mutant to have been born since Decimation (another Marvel event in which 99% of all mutants lost their powers). And yes, one of these factions (the rabid anti-mutant fanatic one) did attempt to 'locate' the child in question by killing all the babies in the infant's home town.
In Camelot 3000, the reincarnation of Mordred experiences a flashback in which King Arthur attempts to drown him as an infant, apparently having learned that his bastard child will one day destroy Camelot. This naturally pisses off his new incarnation enough to instantly turn him from a Corrupt Corporate Executive-type to the Big Bad's new Dragon. Possibly a subversion, as the flashback is induced by Morgan le Fay, who has her own reasons to manipulate him and might've faked the vision to inflame his hatred.
In Prince of Persia: The Graphic Novel, an old prophecy of the invisible prophet of Marv proclaims that, on a certain night in a certain year, there will be born a boy destined to kill all the rulers and the ruled. The rulers of Marv accordingly kill every boy born on that date, except for one who escapes and seventeen years later leads La Résistance to overthrow the rulers. In a Prophecy Twist, the foretold destruction is accomplished by the coincidentally invading Mongols, whose Khan was born at the prophesied time.
It has recently come to light that Thanos' current conquest, detailed in Infinity, is to kill all of his children in fear of one of them overthrowing him, with his last target being on Earth. At the end of the event, that son, Thane, traps Thanos in a "state of living death", and swears to become even worse than Thanos would ever be.
The Queen in "Snow White" may be the most memorable example of this trope. She had little trouble finding the infant Snow White in the first place, but the kindly huntsman who spares Snow White's life and the Queen's ultimate downfall fully adhere to the trope.
In the Percy Jackson and the Olympians fan fic Aska, the Olympians attempt to kill any offspring of the Norse. They are successful until Ayra and her twin brother are born. Thinking that there is only one child, they kill him and stop looking.Big mistake.
Films — Animated
The villainous Shen does this in Kung Fu Panda 2. It goes as well as you'd expect.
It actually works twice. The massacre of the pandas lets Po end up in the right place and the right time to become the Dragon Warrior and receive the training he will need for his eventual fight with Shen (well, he was training to fight Tai Lung, but still). Also, Po remembering his mother's sacrifice during the massacre and coming to terms with it allows him to master the Chekhov's Skill that allows him to overcome Shen's weapons.
Though subverted in that everyone including Shen believes Po will be seeking revenge for this act; in truth he's repressed the memory and is in complete ignorance of Shen's deed.
The Prince of Egypt shows this scenario through an Egyptian-hieroglyphic animation dream sequence, followed by a final confrontation between the Prince Moses and Seti I, his adoptive father: "Sometimes," Seti says, with a look of utter horror on his face at the memory (or is it fear of divine judgment?), "sacrifices must be made...."
In Disney's Hercules, Hades sends his mooks to turn Hercules mortal and then murder him, so that the kid can't derail his takeover plot in eighteen years. But the mooks are interrupted before the task is complete, so Hercules is still alive and has superhuman powers, even though he is indeed mortal. Guess what happens.
Films — Live-Action
Queen Bavmorda did something like this in Willow, rounding up all the pregnant women in her domain and checking each of their children for the mark of the one prophesied to bring about her downfall. The fact that she's defeated not by the the prophesied baby, but by the people trying to keep her safe from her constant attacks makes this a particularly overt Self-Fulfilling Prophecy.
Elana's hair was use in the ritual that opened the portal so, technically, she did have part in defeating the Queen.
The Final Conflict. Damien Thorn (the son of Satan A.K.A. The Antichrist) tries to kill all babies born during a certain time period in an attempt to prevent the Second Coming of Jesus.
The Terminator movies are all pretty much Skynet's attempts at doing this. Further, in the first film, the Terminator hunts down everyone it can find named Sarah Connor. True to trope, all these attempts at taking his life do is better prepare John Connor for his fate.
John Connor wouldn't have even been born if it weren't for Skynet's attempts to kill his not-yet-mother, as the Resistance sent back the man who would be his father to protect her from said attempt.
The Chronicles of Riddick (the film) reveals this is back story of the titular character. The antagonist heard a prophecy that he would be killed by a native of a certain planet, and so wiped them all out. Riddick was found with his umbilical cord wrapped around his neck, tossed in a dumpster. That will mess you up for life, which would go a ways to explaining Riddick's borderline sociopathic behavior.
In The Godfather Part II, the mob boss of the Sicilian town of Corleone kills little Vito Andolini's father over a debt. Then he realizes that Vito will inevitably come for revenge and tries to kill him young, but his mother sacrifices herself. Vito escapes to America, becomes Don Corleone, and returns to Sicily to take his revenge.
In Kung Pow! Enter the Fist, Master Pain (later called Betty) tries to kill The Chosen One when he is a baby. He gets his ass slaughtered by said infant.
The Prequel Trilogy of Star Wars subverts this. There is a prophecy about the Chosen One bringing balance to The Force; while some interpret this to mean that they'll decimate the Jedi who are more numerous than the Sith, the Jedi view, and the one espoused by Word of God, is that they will root out and destroy the Sith Lord lurking in the shadows. Palpatine knows about this prophecy, and when the Chosen One is discovered he doesn't kill him. He spends quite some time befriending and grooming the boy until he could cause a Face-Heel Turn and use him against the Jedi. However, the Original Trilogy then has the son of the Chosen One redeem him and cause a Heel-Face Turn. Palpatine tries to kill the son, and the Chosen One kills him, finally fulfilling the prophecy.
The Sith have their own prophecy, of the Sith'ari, who will both destroy their order and bring it its greatest height of power (the order in which this will happen not being explicitly specified). While Word of God holds that prophecy had already been fulfilled 1000 years earlier, many fans find it more appealing for Anakin/Vader to be the fulfillment of both prophecies, by destroying the Jedi and the Sith.
In Looper, Old Joe finds the addresses of all 3 of the children who share a birthday with The Rainmaker, and intends to kill all of them. He successfully kills one, but is caught before he can kill the second one. He escapes and manages to find Cid, who becomes the Rainmaker, but his attempted murder will inadvertently cause Cid to become the Rainmaker.
In Arthurian mythology, after hearing a prophecy that a child born on May Day, as Mordred was, will destroy him and his kingdom. King Arthur reacts in different ways, depending on the story.
He rounds up all the noble May Babies and sends them away on a rickety ship. The ship sinks, and the only child to survive is Mordred, who is rescued and eventually returned to his parents.
Arthur decides to be Genre Savvy and actually take all the boys to be trained under him. It just so happens that Mordred was the only one of his pages to betray him.
In Arthur, King of Time and Space, Arthur knows the prophecy but takes the position that the mass murder of babies is wrong, and Merlin is Genre Savvy enough to point out that the prophesied baby would escape anyway. Unfortunately, Sir Balin overhears the wrong part of the conversation and tells a scribe to issue a proclamation that all babies born on May Day are to be killed.
This happens several times in Ancient Greek myths. One of the things Oracles tended to predict was someone's child killing the one asking. Usually, trying to kill the child is what caused the prophecy to take place in the first place, at least in the long run. Perseus was such an example.
Cronus and Zeus. Cronus was told that one of his sons would overthrow him, so he swallowed each of his children after they were born. However, the sixth child, Zeus, was hidden from him, and Cronus was tricked into swallowing a stone instead. Zeus was raised in secret and later overthrew his father as predicted.
In another version of the story, Cronus was just paranoid. He thought that since he had overthrown his own father, his children would overthrow him. His attempt at preventing this gave Zeus the motivation to overthrow him.
Zeus himself was worried about being overthrown by his children. When it was predicted that if his lover Metis bore a son he would be overthrown, Zeus tricked Metis into transforming into a fly and swallowed her. Metis took up residence in Zeus' head, hammering armor for her future child, giving Zeus terrible headaches. Metis' child eventually was born, emerging full-grown and clad in armor from Zeus' head, not a god but the goddess Athena.
In another version, Zeus was told that the off-spring of Zeus and Metis would be far more powerful than her father. And indeed, Athena was more powerful than Zeus - but she was also totally loyal to her father and wouldn't dream of overthrowing him.
Zeus was perhaps right to fear, but could've been more Genre Savvy by now, since it runs in the family. Before Cronus, his father Uranus feared an overthrow, and had children capable of doing it sent to Tartarus. Unfortunately, they were all their mother's favorites, and Gaia sent Cronus to take revenge — Uranus's castration was probablyheridea.
Oedipus' parents tried to kill him as an infant due to the Oracle's prophesy that he would murder his father and bed his mother. Unfortunately for them, he got rescued by royals of a neighboring city-state. And so we have the Oedipus Complex...
Paris was also prophesied to cause the downfall of the kingdom and the death of his father. They pulled the same "we couldn't bear to kill him, let's just leave him to die/be found and brought up by a poor shepherd" that they did with Oedipus. This led to him being handy when Athena, Hera, and Aphrodite needed a judge for a beauty contest. Each goddess tried bribing Paris differently, with Aphrodite promising him the most beautiful woman in the world if he chose her, and the rest is history (or, you know, mythology).
In some versions of the story, Zeus engineered the entire Trojan War solely to thin out the ranks of his demigod children so that none of them would overthrow him.
A frustrated King Acrisius goes to the Oracle for want of a son only to be told that his grandson would kill him. When locking his daughter, Danaë in a tower fails, and Perseus is born, Acrisius throws them both in a box and sends them adrift at sea. In the darker versions of the story, Perseus comes back for revenge and subjects Acrisius' entire court to the head of Medusa. In nicer versions of the tale, grandpa and hero make amends, Acrisius is proud of the hero Perseus has become and makes him his heir... only to get killed by Perseus in a gaming accident. Sometimes destiny is just a real bitch.
Considering who the baby's father was, Acrisius got off lucky.
In a subversion, Zeus manages to avert this fate by learning that a certain goddess's (Thetis) child will become more powerful than his father, and proceeds to very carefully not sleep with her. He wound up arranging her marriage to a mortal. The son? Achilles.
Yet another time when Zeus was enough of a Magnificent Bastard to actually be successful in pulling off this maneuver was the case of Typhon. Gaia had supported Cronus in his uprising against his father Uranus, and then Cronus had proceeded to treat his own sons and daughters just as badly — so that Zeus had had to rebel against Cronus the same way. To Gaia, it seemed as if this was just another turn in the cycle of revenge and patricide, so she decided to give birth to a creature who was supposed to defeat Zeus in just the same way as Zeus had done for Cronus and Cronus had done for Uranus. This was the dragon Typhon, and it appeared to be a brutal creature with no redeeming qualities, much like the giants and cyclopes of Uranus's day. But Zeus was able to win his battle against Typhon, thus allowing himself to break the cycle of one tyrant replacing another — for in this case, Typhon would surely have been worse than the god it replaced, not better.
Typhon wasn't the last time. Gaia later attempted the same trick by giving birth to the Giants, snake legged creatures which could not be defeated by gods. Fortunately, Zeus and the others had enough of a warning to start getting hot and heavy with mortal women. By the time the Giants got born, they managed to breed Heracles, who was powerful enough to turn the tide.
It is kind of averted at the end of the Trojan War. Astyanax, the infant son of Hector, is thrown from the walls of Troy so that he won't live to avenge his father's death. It worked. Of course, there was no prophecy involved, but the Greeks probably figured they couldn't be too careful. ...on the other hand, while Troy never rises again, the Greek chieftains who make this decision almost all come to unhappy ends.
In short, Greek Mythology is full of this kind of stuff, although few times do the would-be destiny-screwers explicitly try to kill the child (or its mother) with a weapon or anything, preferring to leave them to die in the wilderness. This was because in Ancient Greek times, killing a blood member of your family was the largest sin imaginable, and doomed you to living the rest of your life hounded by the Furies.
Following this format to the letter is the Greek historian Herodotus's version of the birth of Cyrus the Great. According to him, Astyages, king of the Medes, had a Prophetic Dream that his daughter Mandane would give birth to a son who would destroy his empire. First he tried simply marrying her off to an unambitious vassal prince whom he didn't consider a threat, but when she got pregnant, the dreams resumed. When Cyrus was born, Astyages arranged for one of his generals, Harpagus, to kill the baby while Mandane would be told that her child was stillborn. Instead (for the reasons described above, and also out of fear of Mandane should she ever find out), Harpagus entrusted the job to a herdsman. But the herdsman's wife really had just had a stillbirth, and they left their own dead baby on the appointed hillside and kept Cyrus. When Harpagus's deception emerged years later, Astyages punished him by killing his son and feeding him to Harpagus at a banquet. This caused Harpagus to side with Cyrus in his rebellion against Astyages and help him conquer Media, making this another of your good old Self-Fulfillling Prophecies.
In Hindu Mythology, the Avatar Krishna's uncle, Big Bad Kamsa, hears a prophecy that his nephew will kill him. So he imprisons his sister and kills her 9 children one after another as soon as they were born. Krishna, the 10th child, escapes at birth. It does not end well for him.
King Jehoash (usually rendered in the short form "Joash" in translations) of Judah escapes the blade when his aunt protects him as an infant from his grandmother Athaliah, who seeks to kill all heirs to the throne so that she could stay queen after her son Ahaziah died.
Even before that, the Book of Exodus describes the Pharaoh ordering the elimination of every newborn son, to cut down on the Israelite growth (rather than taking out a specific individual.) However, his own daughter winds up rescuing one of them, Moses, who grows up and is called by God to free his people.
Lord Voldemort knew a certain child or another would have the power to destroy him, and acted accordingly. Unfortunately, incomplete knowledge of the prophecy on his part rendered it self-fulfilling.
An example of this occurred in the Wheel of Time series, where the prequel novel New Spring described attempts by the forces of the Dark to find and kill Rand right from the day he was born. Since they weren't entirely sure how old he was at the time, they went around killing pretty much every young male who showed signs of being a channeler.
An interesting little Word of God statement mentions that this royally pissed off Big Bad Ishamael badly enough that he messily killed the head of the Black Ajah at the time.
A large part of the prequels to David Eddings' Belgariad deals with Polgara's task of safeguarding the line of young Rivan kings from Torak's assassins. In the main story, Asharak gets the full treatment, as Garion enacts a very specific form of revenge upon him for the deaths of his parents.
This is touched off by an earlier "Nice Job Breaking It, Herod" when Torak sent assassins to eliminate the Rivan royal family. Polgara's charges are the descendants of the one son who inevitably escaped the slaughter.
John Moore's Heroics for Beginners mentions a villain who succeeded to the throne of a kingdom by slaughtering the rightful ruler, his wife, their children, and so on. The catch was he couldn't get all of the children — even though he'd been wise enough to schedule an assault on every potential heir and his or her family. Amazingly, the villain was Genre Savvy enough to not attempt to break it; not because he didn't want the successors dead, but because if he did kill everyone in the necessary age groups — teenagers and under — he'd cripple the country's economy down the road. Instead, he went psychotically paranoid and ended up locking himself in a nigh-inaccessible room.
The Horse and his Boy: The corrupt official Lord Bar in King Lune's court in Archenland learned of the prophecy that one of the twin newborn princes would someday save Archenland from the greatest danger that would ever threaten it. Even though Bar had no idea what this danger would be, on the off-chance it would be something he would cause, he decided to try to get said prince out of the way just to be on the safe side. Too bad for him Aslan was watching over things...
Let's not forget Macbeth (the Shakespeare version): Because the witches have told him that the offspring of Banquo will be kings, Macbeth decides it's a good idea to have Banquo and son murdered. The murderers kill Banquo, but naturally screw up the important part of the job. It's a variation on the trope, because Macbeth is not killed or overcome by Fleance, but his descendants later fulfilled the prophecy (at least according to the erroneous genealogies of Shakespeare's time).
Inverted in Sarum, where a Neolithic chieftain is so obsessed with a prophecy that he'll never sire an heir of his own unless it's by a "woman crowned in gold", that he raids other tribes, forcibly marries their highborn women, and then has them executed when they fail to conceive within a month. By the time a blonde woman arrives in the area, he's made enemies of all his tribe's neighbors and killed most of his advisors for trying to discourage this bloody practice.
Bizarre Alien Biology example: The Pak protectors, from the Known Space novels of Larry Niven, are compelled to destroy even infant Pak that aren't related to them because they don't "smell right", thus eliminating their own offspring's competitors. The fact that their inter-bloodline feuds tend to leave their planets devastated and every combatant's bloodline extinct, qualifies their entire species for this trope. Also a complete failure of biology, as any Pak that successfully exterminated all rival genetic lines would then watch its own bloodline expire from inbreeding depletion.
In Fiona McIntosh's Royal Exile, this happens twice: the first is at the very beginning when King Brennus has another baby killed in order to protect his newborn baby daughter, and even the mother doesn't know what's up, and later on when the warlord orders all boys around the prince's age to be killed throughout all the kingdoms.
In The Graveyard Book, the Jacks of all trades hear a prophecy that some toddler is going to be their doom. They send in an assassin, who kills his whole family but fails to get the baby. You can guess where this is going.
Mad Emperor Yuri of Barrayar from the Vorkosigan Saga attempted to kill off everyone else who might have a claim to the Imperium, but he missed Aral Vorkosigan. (He did get Aral's mother and older brother, though.) He also didn't bother trying to kill Aral's father, Piotr Vorkosigan, who wasn't in the line of succession. (This is further evidence of just how mad he was.) Piotr threw his support behind Yuri's brother, who was also missed, and started the civil war that took Yuri down. Two years later, Aral, aged thirteen, got to take the first cut in the long drawn out execution of the ex-emperor.
In Gwenhwyfar by Mercedes Lackey, which is based on Arthurian Legend, the protagonist hears of how Arthur, under the advice of the Merlin, killed all newborn babies in the kingdom (it's even implied that this is the reason why Gwen's mother dies while giving birth to her baby brother, who also dies). Toward the end of the book, Medraut reveals that Arthur was trying to kill his illegitimate (and incestuous) son, but Morganna and Anna Morgause foresaw it and worked a spell that caused Medraut to be born a few months early, saving him from Arthur's wrath.
King Erius in The Bone Doll's Twin kills off female relatives who can challenge him for the throne (traditionally held by a queen due to divine mandate). He spares his baby sister Ariani, but has no intention of doing the same for her daughter - except that the daughter is passed off as stillborn and then raised in the guise of her dead twin brother.
In The Idhún's Memories, a trilogy by the Spanish writer Laura Gallego, in the world Idhún, Ashran the Necromancer uses an astral conjunction to wipe out all dragons and unicorns after hearing one of each will destroy him. Eventually, one baby dragon and unicorn are rescued and sent to the Earth through magic, which will end up killing him.
Subverted in A Song of Ice and Fire. The maegi Mirri Maz Duur magically kills Daenarys Stormborn's unborn son in utero, both for revenge against the father and because the unborn child is prophesied to be the Stallion That Mounts the World, an unstoppable city-smashing warlord. While it doesn't exactly turn out well for Mirri in the end, she DOES successfully prevent the boy from being born and fulfilling whatever his Super Special Destiny was supposed to be.
We shall see, his mother still lives, and she might well wind up taking her son's mantle and become the Stallion that Mounts the World. Prophecies in A Song of Ice and Firehave a tendency to come true.
In vengeance, Daenerys had MMD burned alive. Her death by fire hatched the three dragon eggs Daenerys had. A single dragon can destroy a city or an army withn seconds, and Daenerys considers them her babies...
Was a large part, although hidden, in the Ender’s Game series. Specifically in Ender's Shadow: Bean was the only survivor of 20-odd children. He then grew up to assist in the total destruction of the only other sentient species.
The Earthsea Trilogy has a king who received a prophecy his empire will fall because of a person from the former royal house. By then, there were only two children left; a boy and a girl. He was afraid to kill them (Royal Blood), so he banished them to a desolate island. They survived until old age. Then, one day, Ged is washed ashore. The girl gave him an old family keepsake...
In Dune Emperor Corrino was told by the The Spacing Guild to kill Paul Atreides to ensure his control over Arrakis. But Baron Harkonnen only killed his father Leto Atreides, while he left Paul and his mother in the desert. This backfired spectacularly, as Paul soon become the leader of the Fremen, and leads them in an all out war against the Harkonnens and successfully overthrew the Emperor.
Again, Jesus of Nazareth (the TV series from the 1970s) has an AWESOME Peter Ustinov play the trope-name scenario perfectly. First seen as an Affably EvilAdipose Rex feasting and cynically chatting with Roman envoys about destroying newborn Messiahs 'like a new born scorpion, underfoot', he steadily degenerates over the course of the first two hours of the series as he fears the coming rival King of the Jews, finally falling into a gibbering near fugue state when he at last horrifies his court with the order to 'Kill! Kill! Kill them all! Kill! KILL THEM ALL!'
Also, the Xena: Warrior Princess episode "Cradle of Hope" featured a baby prophesied to be the next king. In that case, Xena heads off the infanticide by convincing the king to adopt the child and make him his lawful successor.
There's also the complete reversal in Xena: Warrior Princess where someone sends a baby floating down the river to save her life... from the hero, because the baby is prophesied to bring about DOOM. While it's never entirely clear, there are hints within the narrative that perhaps the ensuing destruction could have been avoided if the baby had been brought up by a loving mother instead of having people try to murder it all the time.
Not a baby, but the Archangel Michael says that as long as Xena's daughter is alive, Xena has the power to kill the Greek gods. What do the gods do? Attack Eve. What does that cause Xena to do? Kill the gods. Xena was never particularly fond of the gods in the series, but would she have gone on a killing spree if they hadn't endangered her daughter?
This happens in Legend of the Seeker, where Darken Rahl finds out about Richard and attempts to find and kill him while still an infant, by slaughtering every first-born son in his hometown.
The Rahl family in the books has this as a general policy for their own children who are ungifted. In the case of those that just can't use magic, it's because they're useless as an heir. For the ones who're pristinely ungifted, it's because their immunity to magic can make them a threat.
In Babylon 5: The Lost Tales, John Sheridan is warned by Galen the Technomage that a young Centauri prince (and the grandson of B5's Caligula-expy) will one day inherit the throne, become a megalomaniac and invade the Earth — obviously, he must be killed to protect innocent lives. However, the trope is subverted when Sheridan decides to raise the prince himself and teach him a better way. Furthermore, Sherdian gets Galen to all but confess that was his true plan all along.
Played with twice on Merlin. Uther is so desperate to rid magic from the land that he drowns all the children who may have inherited magic. One baby escaped, the half-sister of his illegitimate daughter Morgana, who would later turn Morgana against him and start the chain reaction to break his spirit. The other example is his genocide of the dragonlords. One does escape, and winds up fathering Merlin, who is destined to bring magic back to Camelot.
In Game of Thrones, either Cersi or Joffrey (it's ambiguous which one of them) orders the slaughter of every single bastard child Robert Baratheon fathered. Such children may have posed a threat to Joffrey's rule. Of course, one escapes.
In Yoshi's Island DS, Bowser and Kamek kidnap all of the Mushroom Kingdom's babies in hopes of finding the seven Star Children.
Variation in Dragon Quest IV: Aware that The Chosen One is currently growing up somewhere in the world, the monsters attempt various plans to track down and destroy that child. One of these plans gets the attention of Ragnar, who learns of the prophecy while thwarting said plot and leads him to set out in search of said hero. Later, it's revealed that Ragnar is one of The Hero's Chosen Companions...
Later, the monsters find the hidden village where the Hero is being raised. They attempt the obvious solution, which naturally doesn't work.
And in Dragon Quest V, Grandmaster Nimzo and Bishop Ladja try to kill the "Legendary Hero" because they believe that one of the Hero's children (preferrably the son) would grow up to be the true Chosen One. Since the children have been well-hidden by the residents of Gotha Castle, Ladja has to petrify both the Hero and his wife and wait until the child grows up. As a statue, the Hero is sold to the Porgie family, and is forced to watch as their child, Georgie, grows up... and then gets mistaken for The Chosen One and kidnapped by monsters... all the while the twins are growing up sheltered until they find their father and restore him to flesh and blood, and they would soon save the day... with help from the Hero's son, of course.
The backstory of Jade Empire showcases the Emperor wiping out the Spirit Monks to the last, so that none will remain to protect the Water Dragon, allowing him to enslave her for great power. However, he missed you, the Player Character, who was hidden away and raised by the Emperor's brother. This trope then turns out to be invoked and subverted; the only reason the Emperor's brother saved you was so that you would have the motivation and drive necessary to overthrow the Emperor, at which point his brother steps in, bumps you off, and sits his ass on the throne.
In The Legend of Dragoon, the Black Monster, Rose, kills the Moon Child every 108 years to prevent the birth of the Virage Embryo. Dart's hometown Neet was razed as a result, seeing as how the Moon Child, Princess Louvia, resided there. The only problem? Louvia had a twin, Shana, and she was in fact the real Moon Child. Oops.
Fable II begins with Lucian murdering your sister and attempting to do the same to you because you have hero's blood and have the potential to unravel his plan. It would've been a very short game if he'd managed it.
Zeus in God of War is told of a marked warrior who will bring about his downfall. Naturally, he kidnaps the nearest birthmarked kid and imprisons him in Death's Domain. Unfortunately for Zeus, the kidnapped kid's brother is Kratos, who gets a tattoo in the image of his lost brother's mark. It's all downhill from there.
In Ni No Kuni, Oliver is targeted with a curse when the Big Bad learns it is Oliver's destiny to interfere in their plans, but the curse ends up killing Oliver's mother instead. Oliver learning that he has the chance to bring his mother back from the dead is what gives him the resolve to become a hero.
If I hear about a prophecy or prophecies that state that a child will be born in a certain place with a birthmark or some other sign who will bring about my downfall, I will not immediately send troops to kill the child and its entire family. Instead, I will wait until the child is about five, while keeping it under surveillance, and then have it kidnapped and killed. Once this is done, I will bury the body in a careful location so the body does not get eaten by wild beasts, resurrected by the good guys or wash up on some foreign shore. And for everyone's sake, I will make sure that the child is actually dead, instead if just stabbing it once or suffocating it. Bullets are very helpful, especially fifty-fold.
To their credit, the Fire Nation realized fairly quickly they missed Aang, and spent a century trying to track him down. (Most of them got much less concerned as the years went by and the Avatar never showed up.)
Also, there's the Fire Nation's campaign of capturing and exterminating waterbenders of the Southern Water Tribe. (The exact reasons for this are not explained, though theories abound that they were trying to stop another Avatarnote If the missing Avatar had died in the interim, the next in the cycle would be from the Water Tribe. And the Southern Water Tribe was an easier target than the larger, more militarized Northern Water Tribe. and/or wipe out resistence.) They missed Katara, who went on to train Aang and play a part in their downfall...though it should be noted that they only missed her because her mother told the Fire Nation commander that she was the last waterbender, and died for it.
Sonic Underground featured Sonic the Hedgehog and two siblings being hidden from Dr. Robotnik by their mother the queen.
She-Ra: Princess of Power: Hordak kidnaps Princess Adora and trains her as a general, until He-Man shows up and touches off her Heel-Face Turn into She-Ra. It might have worked better if Hordak and Shadow-Weaver had not, for reasons known only to them, raised Adora to have a fully-functioning sense of justice and morality which requires them to deceive and magically control her to retain her loyalty... but the show is aimed at kids, after all.
Actually, Hordak (after trying to kidnap both babies) and Shadow Weaver left most of Adora's early upbringing to Shakra. ("The Caregiver", PP 077) Shakra is a kind, loving person, and instilled much of her own sense of morality in Adora, regardless of Shadow Weaver's spellcasting. Goes to show what happens when the bad guys don't pay attention to what's going on under their noses.