In fiction and in the media in general, both heroes and villains usually agree on one thing: they Wouldn't Hurt a Child.
This creed exists for various reasons: it may be because Children Are Innocent, and thus should be protected and kept out of harm's way at all costs; it may be because, to Moral Guardians, seeing a child being brutalized is Harmful to Minors and thus should be avoided; it may also be because even writers mostly disagree with the idea of writing about harming a child.
But sometimes, some people just don't agree with that. Or just don't care. And, they do hurt children, sometimes even kill them, in defiance of the rule of Infant Immortality. Indeed, the act of harming a child usually comes off as the ultimate act of villainy and it takes a very specially evil character to do this.
Needless to say, this trope is almost always a Kick the Dog moment. Hence, the presence of Would Hurt A Child is often telltale of a Crapsack World or at least a Darker and Edgier series. However, it is surprisingly easy to subvert this trope simply by using Kids Are Cruel (the flip side of Children Are Innocent) and combining it with Pay Evil unto Evil. Want to go all the way? Make the children creepy or, even better, make them Enfants Terribles and, this time, hurting said children will look much less as a Moral Event Horizon crossing, even though there will always be some Moral Guardians or Papa Wolf / Mama Bear to complain. This may also be done by a Complete Monster to establish that even the Big Badhas lines s/he won't dare cross. Naturally, the Friend to All Children sees this type of character as a mortal enemy.
In Western works, this trope is rare and almost always done off-panel when played straight (read: when the violence towards the child isn't being stopped in the nick of time and causes actual damage). In Japanese fiction, child brutality is more common.
Important Note: This trope is about adults physically hurting children, fatally or not. The following are not examples: slapping, butt-warming and general discipline from parents to their children (that's Don't Make Me Take My Belt Off), psychological/verbal abuse (very common but not that trope), abduction (only applies if the child dies or gets effectively hurt), child on child violence (that's Kids Are Cruel), exploitation for profit (that is Financial Abuse). Violence to teenagers isn't an example either since teenagers are physically stronger than children and lack the "completely defenseless" element, especially if Teens Are Monsters. However, teenagers harming children applies.
There is also an interesting Double Standard when it comes to characters applying for this trope, since they are almost Always Male (Oddly enough, this is not representative of real life, as women are more likely to abuse children than men). Rarely are women described as being physically violent to children. Even rarer are the instances when they actually kill them. Indeed, killing children is among the few things that permanently prevent a woman from a convenient High Heel-Face Turn. Extra points if the killing is done directly and at the woman's hands (i.e. stabbing, strangling etc...). Compare Pćdo Hunt, another child abuse trope where female perpetrators are similarly unheard of.
A subtrope of Kick the Dog. See also Child Hater, who hates kids but isn't necessarily physically abusive and Nice Job Breaking It, Herod!, which is often an extreme version. Contrast Infant Immortality and Wouldn't Hurt a Child. Compare Kids Are Cruel, Children Are Innocent. Related to Eats Babies and Child Eater. Usually applies to the Sadist Teacher.
Perhaps Joker's most notorious moment of this came during the "No Man's Land" mega-arc, where he plotted to kill all the newborns in Gotham City on New Year's Day, just so that he could destroy the already fragile spirit of Gotham's citizens.
Fantastic Four villain the Wizard had absolutely no qualms about performing an experiment on Franklin Richards that had a high probabilty of causing Franklin's death. Fortunately for Franklin, the Wizard's current partner the Mad Thinker would not hear of it, dissolved their partnership and contacted the Thing, who helped him defeat the Wizard.
Winnowill in ElfQuest imprisons, humiliates and tortures the Wolfriders, but it's only when she threatens Cutter and Leetah's children that she really crosses the line. Then there's her 'relationship' with her son Two-Edge.
One of the first things the Plutonian does in Irredeemable is vaporize a child.
Spider-Man villain Carnage has no qualms about who he kills, children included. During his rampages, child corpses are often among the dead, and in his youth he torched an orphanage.
Sabretooth from X-Men is known to attack, murder, and sometimes even eat children. In one issue, Deadpool is in a cabin with him and he opens a closet to find a little girl tied up. When he asks about this, Sabretooth replies that he's saving her for later.
Dodge from Locke & Key has no problem pushing a child under a school bus because he's figured out too much.
In Cerebus the Aardvark, this starts showing up once the Cerebus Syndrome kicks in, with the most notorious example being Pope Cerebus blessing an infant after his mother begs Cerebus to do so and then hurling it away to illustrate the point that "you can get what you want and still not be very happy."
Doctor Doom showed no hesitation in trying to murder the Hulk's young son, Skaar, and at the end of Avengers: The Children's Crusade, he kills the young Cassie Lang. On the other hand, God help anyone who tries to hurt one of Latveria's children when he's around (or the Richards kids. Especially Valeria).
In one issue of The Spirit, two bank robbers plan to kill all witnesses to their crime — including a little girl just coming around the corner. With tommy guns. note Frightened, she falls down — and survives.
In Superman, Catherine Jane "Cat" Grant's son Adam Morgan is first kidnapped by Toyman (alongside other children), then is stabbed to death when he attempted to escape from him.
My Little Pony: Friendship Is Magic (IDW): Queen Chrysalis has made it quiteclear that she doesn't intend on letting the Cutie Mark Crusaders leave. Not to mention a luvcat kitten was seen before Chrysalis and her soldiers took over the village.
Marcus Brutus in Asterix and Son fits this trope. He burned down Asterix's village, and nearly kills the baby boy Asterix is trying to protect because the boy is really Ptolemy XV Caesarion, the son of Julius Caesar and Cleopatra, and that killing would solidify Brutus' power in Rome. A rare departure from the comedy of the usual comics.
A very rare heroic example: X-23 confirmed to Valeria Richards that she killed children during her time as a Tyke Bomb assassin-for-hire. This changed, however, after her escape from the Facility. She did later kill symbiote-infused clones of herself in Blackheart's service, who could technically be considered children.
And the Facility members who tortured her in the first place certainly qualify. Zander Rice and Kimura both subjected Laura to horrific physical abuse from the time she was seven years old. Rice also sent her to kill his illegitimate toddler son Henry (she ultimately refused to carry it out), while Kimura tried to kill Laura's cousin, Megan, by slowly pushing her finger through her heart just to punish Laura over her escape.
The Runaways frequently manage to run into villains who are willing to hurt kids. This often leads to humiliating defeats at the hands of Molly and Klara.
The celebrity team X-Force (later called X-Statix) overthrew their former coach in part because he planned to hand over a little boy with healing powers to pharmaceutical companies to be dissected.
Norman Osborn visited Baxter Building to speak with Reed in one of the Dark Reign stories (Dark Reign: Fantastic Four Vol 1 4). Unfortunately Fantastic Four team was away at the time and the only people left in the building were Richards' children, Franklin and Valeria. Visit is tense, but more or less civilized, until Franklin showed up with Spider-Man's mask. It does not take long for Norman, known psychopath, to start shooting at kids.
In the X-Men graphic novel God Loves Man Kills, the evil of Stryker and his Purifiers is established on the very first page as the Purifiers kill two young mutant children, the older of whom might be 10, the younger of whom is six or less. At the end of the book, Stryker himself aims a gun at the adolescent Kitty Pryde.
Judge Dredd: No crime is too low for Judge Death—he is after all an Omnicidal Maniac par excellence. At one point he purposefully sought out orphanage shelters to kill all the children he could find specifically to piss of Judge Anderson, to whom hurting children is a major Berserk Button.
In DC Comics' Legends, Glorious Godfrey goes as far as slapping a child when she tries to speak reason to a crowd of adults that were surrounding the superheroes at the climax of the story, ready to let them have it.
In Cable & Deadpool Deadpool states that he would kill a child—wouldn't like it, but would do so, as he's a merc and this is his job. He later attempts to kill a child version of Cable, although he's been brainwashed and has just rescued Little Nate... this all actually Makes Sense In Context.
In the Dashverse story Hot Heads, Cold Hearts and Nerves of Steel, Sombra has his minions kidnap every foal in Ponyville and several other towns so he can drain their life forces to make himself stronger.
His bushwoolie Mooks have no problem with harming foals, and the two that Pip, Alula and Dinky encounter try to eat them.
Hitman Miami: In mission (chapter) seven, 47 (the protagonist) needs to get money for his supermarket shopping. The only way is, apparently, garrotting children in the toy section and stealing their change.
Armitage III fanfic Gods And Monsters features a female protagonist who is more than willing to kill children. Even the author called this out as being hard to pull off.
Reality Is Fluid: An Undine psi master shows Eleya images of Federation, Gorn, and Klingon warships, which Eleya knows to be Iconian fakes, bombarding Undine spawning pools and killing their hatchlings.
The Matrix/SupernaturalHunting Series in part 3 - Hunting and Saving has vampires that in the past killed/drunk from kids and would have killed one of the future progtagonists if John hadn't been hunting that night.
In "Dear Scootaloo", Feather Duster had no qualms about firebombing an orphanage and tossing foal Scootaloo off a cloud.
Film - Animated
Reconstructed in The Incredibles. Helen has to explain to Dash and Violet that yes, real villains would hurt a child. And they do. Then again, the kids can fight back... The fact that this is the case is also a contributing factor to Mirage's Heel-Face Turn.
The other PG Pixar Film, Up, has the villain send dogs to attack the kid there, and before he died, almost shot the kid as well. Pixar seems to tell people that villains can, and WILL, harm and kill children if they have the option.
Speaking of Pixar, a plan involving Randall and Waternoose in Monsters, Inc. may not have specifically aimed at killing children, but the results of the Scream Extractor seem anything but harmless.
The Great Mouse Detective: The Faux Affably Evil Ratigan is revealed - in song, no less - to have drowned widows and orphans. Near the end, during the Big Ben battle, he's shown kicking Olivia off a large gear, directly into the path of being crushed by two other gears. Luckily Basil is able to rescue her, just barely in time.
The Hunchback of Notre Dame: Judge Claude Frollo, in the first few minutes of the film, would have dropped baby Quasimodo down a well if not for the intervention of the Archdeacon, who demanded that Frollo raise the infant to atone for killing Quasimodo's mother.
Captain Hook of PeterPan puts a bomb in a house full of children and makes a teenage girl walk the plank.. and just watch him go all Ax-Crazy in the climax against Peter.
Madam Mim in The Sword in the Stone tells 12-year old Wart she's afraid she's going to have to kill him.. by turning herself into a cat while he's transformed into a little bird. It's downplayed because Merlin intervenes in time, but still.
Shere Khan in TheJungleBook is insanely devoted to slaughtering a certain human boy.
ParaNorman: Agatha, a young girl who can talk to dead people like Norman can, is executed when the town's elites come to the conclusion that she is a witch.
And the modern day townspeople who were enthusiastically planning to BURN NORMAN TO DEATH.
Recess: School's Out shows us that the villains will attack children, though they fail for the most part.
The Grand Duke of Owls in Rock-A-Doodle, near the film's climax, asphyxiates child protagonist Edmund when the boy-turned-kitten refuses to give up, in a supremely dark example of Mood Whiplash. A combination of Disney Death and All Just a Dream makes it better, but it's still shocking.
King Candy in Wreck-It Ralphtried to delete Vanellope from the game's code, and when that failed turned her into a glitch. Then when she races him, he slams into her, tries to knock her out using a dislodged gearshift and finally pushes her in front of his car intending to smash her into a stalactite. This trope may be slightly out of place due to all characters being ageless video game characters, but Vanellope was programmed as 9 years old.
The hyenas, who nearly kill Simba and Nala after they wander onto the elephant graveyards (although averted when Mufasa shows up) and Scar, who shows no qualms about putting young Simba in extreme danger to achieve his ultimate goal – becoming king of the Pride Lands. First, he tricks Simba into the gorge below Pride Rock before sending – with the hyenas' help – a stampede of wildebeests through, forcing Simba to hang on for dear life. Mufasa is able to rescue Simba, but this results in Scar murdering the exhausted Mufasa by throwing him back into the stampede. Later, as a mourning Simba is exiled from the Pride Lands, Scar sends the hyenas after the cub; Simba's death here is averted as he makes his getaway.
Jack Skellington from The Nightmare Before Christmas, apparently. A line from "Kidnap the Sandy Claws" suggests Jack will beat a trio of children if they harm the eponymous Claws, which is odd considering nothing in Jack's behaviour hints he'd do such a thing.
Actually, Jack's not the one who fits in this category. The trio of children in question - Lock, Shock, and Barrel - are the minions of the Big Bad, Oogie Boogie. They don't know Jack very well, but they live with Oogie. Jack wouldn't actually hurt kids, Oogie would have no problem with it. It's more likely that the trio assume that if they screw up their job, Jack will punish them the way Oogie would.
Many people in the Black Tide Rising series comment on the fact they don't like killing the zombie children, and while we don't see it happen the characters clean up the remains of children on occasion.
In The Red Vixen Adventures, this is part of ex-Space PirateChild Soldier Alinadar's background. After her own family was murdered by pirates when she was six, she was taken aboard their vessel and trained up to participate in boarding actions, forced to hunt down other children in the hidden spaces of the ships the pirates attacked. Unusually for the trope, she managed a successful Heel-Face Turn and was exonerated from her actions when she eventually went to trial, the judges noting that as a child herself at the time, she had little choice but to obey orders or die.
Country music has approached the topic in several hit songs about child abuse. The video for Martina McBride's "Concrete Angel" comes the closest to actually showing parent-on-child abuse on-screen - a young boy watches as shadows on a wall depict a woman (an actress shaking a stunt dummy) shaking her daughter viciously. "Alyssa Lies" by Jason Michael Carroll strongly implies that a young girl had been viciously beaten by her father.
In The Bible, King Herod did this in order to try to kill Jesus. Didn't work.
Earlier, Pharaoh killed Hebrew sons to keep the Hebrews from becoming strong enough that in case of a war they could join the enemy and fight against Egypt. Fortunately for the Hebrews, Moses escaped slaughter.
And God Himself kills the firstborn of Egypt as one of the Ten Plagues, as well as David and Bathsheba's firstborn. In His case, it's the Omniscient Morality License: He's Lord over all creation.
Some of the laws in the Old Testament requires parents to have their children stoned to death for being disobedient.
In Samuel I, King Saul is ordered to exterminate the Amalekites: every man, woman, child, and animal. He is removed from God's favor when he disobeys by being insufficiently thorough in the genocide.
Many Greek myths punish a parent by slaughtering their children. Probably the best known example is Medea with the addition that the children in question were her own and their deaths were to get back at the philandering Jason.
Gudrun from Norse Mythology kills her own children who she birthed to Attila the Hun and puts them in his food.
Melissa Coates slapped a boy booing prior to her challenging Mercedes Martinez from the WSU Championship. Hailey Hatred went so far as to push over two adults and the life a little girl out her seat and throw her while in search of something to hit Martinez with.
Bryan Danielson threatened to backhand of a girl flipping him off while he was cutting a promo in Ring of Honor. She started flipping him off again while he continued his promo, leading to him getting out of the ring to confront her, with the crowd chanting for her to "fuck him up".
Shadowrun: MegaCorps that want stable, loyal cyborgs have learned that children make the best candidates. HMHVV-infected are cannibalistic so it's assumed that they'll eventually eat children. Mr. Johnson may want your group to kidnap, hurt, or kill a target child for reasons he's unwilling to divulge.
The Dread Emperor, a villain introduced in the Splat book The Book of Vile Darkness, not only gladly hurts children, he uses this behavior to benefit him in the most selfish way. An imposing, two meter tall man in golden armor, the Dread Emperor keeps children chained to his armor at all times with any damage done to the Emperor himself transferred to the children via the armor's magic. An unrepentant Serial Killer, the Emperor uses these children as a bait for any heroes foolish enough to take him on and does not limit his hostilities to children; he will often destroy entire city blocks when he's a mind to. When a hero challenges him, the Dread Emperor feels no compunction slaying hundreds simply to kill a target or mentally enslaving any civilians nearby and using them to attack his opponent for him.
The 4th Edition introduces hideous monsters called banderhobs who kidnap mortals, some of them actually taking children from their bed at night. (The illustration for the creature in the Monster Manual 3 shows one about to do just that.) Where they take their victims and what they do with them is a mystery.
Stand Up Comedy
Mike MacDonald, when he and his wife were trying to conceive a child, noted in his act he was going to do his best not to hit his kids, ever—unless, you know, they were coming at him with a knife or something.
I don't wanna be one of those liberal parents who gets stabbed to death by their kid while saying, "Son, I'm sensing hostility OH GOD!"
One of Bernie Mac's punchlines in his act was threatening to beat his kids "till the white meat shows".
Denis Leary, in a larger bit about celebrity entitlement, said that he was looking forward to beating the shit out of his kids.
That's therapy for you: mowin' the lawn while cryin'.
In Pokémon Live!, Giovanni is perfectly willing to kill Ash with MechaMew2's Hyper Beam, and he engages him in a fistfight shortly before that.
Universal Orlando's Halloween Horror Nights implied this with their 2010 haunted maze, The Orfanage: it's heavily implied that the entire house takes place after the orphanage has burned down and you're being assaulted by the ghosts of the children, with various imagery and audio hinting at various tortures that the children were put through by their caretakers until Cindy demonstrated her abilities and burned down the orphanage with all the kids trapped inside.
Kirei Kotomine of Fate/stay night rounded up all the surviving orphans of the Fuyuki Fire and cut off their limbs before sealing them in coffins that drained their prana. They were alive and aware for the entire ten years between the two wars.
Zouken Matou has no issues with Shinji treating Sakura harshly or raping her. In fact, he has gone to significant lengths to break her psychologically.
In Saya no Uta, Yousuke Suzumi dismembers his young daughter and rapes the young-looking Saya after getting the same type of Agnosia the protagonist suffers from.
Al Chest Breach. Played for laughs. Word to the wise: don't try talking over Al.
Ronald Dillinger, the child whom Doctor Dan (played by Al) hunted down and killed Ronald because he escaped life as a slave.
The ancient black dragon in The Order of the Stick intended to kill Varsuuvius' children, and managed to hurt them before V showed up to stop her. She notes that people don't think anything of killing dragon young, such as when V killed her (young adult) son.
Rich brings up a good point about dragon wyrmlings having stats and therefore indicting many PCs for slaughtering dragon children despite them being clearly sentient. The mother dragon's whole beef was with V killing her son.
Then again, the reason most people find hurting or killing children to be offensive (at minimum) is because children are usually helpless, defenseless, harmless innocents, four things which a Young Adult Black Dragon most emphatically is not. A young adult black dragon is a significant threat to a party of humanoid adventurers; two humanoid children are not remotely a threat to an adult Black Dragon.
Also applies in the prequel Start of Darkness when the paladins attack Redcloak's village, emphasizing their brutality. On seeing a teenaged goblin attempting to defend his even younger brother and sister, a paladin on horseback is gleeful at the opportunity to take out three in a row and use her great cleave feat. Redcloak's six-year-old sister is killed while trying to hide, and another mounted paladin chases down his little brother, blinds him in one eye, and attempts to kill him before Redcloak comes to his rescue.
Mavra Chan in Terinu was shown onscreen beating the life out of the title character (when he couldn't even fight back) and in a flashback having him set upon by bloodsucking animal as part of this Training from Hell. Then there's Admiral Blake, who sends assassins after the 15-year old boy...
In Axe Cop Babysits Uni-Baby, Dinosaur Soldier summons two cyborgs to "punch (Uni-Baby) any time she would cry or make a ruckus." This trope is subverted in that Axe Cop and his partner are not evil, and are in fact the heroes of the story. The story was originally written by a 7-year-old who makes no distinction between children and adults, and considers the act of punching someone in the face to be fairly equal-opportunity. Instead of a cyborg punching a defenseless infant, it's supposed to be a cartoon cyborg punching a cartoon baby.
Kore in Goblins murders a child in the first scene he appears in. The child in question is an orphan who's been Raised by Orcs, and to Kore's twisted perception of good and evil, anyone who potentially has sympathy for the 'monstrous races' is guilty of evil through their passiveness.
In Unsounded the Red Berry Boys, particularly their leader Starfish. They use human bodies as smuggling vessels, and are paid by the body. Starfish realizes they can stretch their product further by using smaller bodies.
In one of his Counter Monkey episodes, Spoony warns that if you ever DM a game, never put the players in a situation where they come across some orcs looking after orc babies. Because inevitably, someone won't want to kill the babies, but someone else will.
Whateley Universe: the Mafiosi in "Mimeographic" who were perfectly willing to kill a twelve-year-old boy unless the kid attempted to commit murder for them.
Also, Jared Reilley's father, who - once he decided for no rational reason that Jared might not be his son - tried to beat Jared to death with his bare hands. He only failed because Jared manifested as a mutant under the stress.