Surprise! Two of the main characters have just had a child! I bet you are surprised, since they didn't go through pregnancy or anything, might not even be dating, and the kid is already 14!
It must be the Kid from the Future here to Set Right What Once Went Wrong! A child the characters have yet to have has traveled back in time to save their parents for some reason. Great for pairing up characters who have yet to even show any interest in each other since now they must get together Because Destiny Says So. Also a way of working in a Distant Finale into the plot of what has already come along.
If the series involves a Love Triangle, or, worse yet, an Unwanted Harem, expect all hell to break loose as those involved try to figure out who the child's mother or father is.
This trope is also used in Fan Fiction (especially Fix Fics), often to push together the author's OTP, pair the Mary Sue with her chosen love interest, or even as the origin for the self-insert or Mary Sue.
An extreme form of Plot-Relevant Age-Up. Can develop into a full-blown Spin-Offspring.
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Anime and Manga
Trunks from Dragon Ball. In his case, his parents might have had two scenes together at that point and his mother had been with a different guy for about ten years. Goku's reaction is shock and disbelief. Neither of his parents actually know who Future Trunks really is until after they've gotten together, as neither Goku nor Piccolo (who overheard due to his superior hearing) said anything.
Chibi-Usa and Diana from Sailor Moon. As a result, this trope is sometimes referred to as "pulling a Chibi-usa".
The entire plot of the manga/anime series Mother Is A Fourth Grader - a ten-year-old having to deal with taking care of her infant child who has fallen through a time-warp from the future.
Chao Lingshen in Mahou Sensei Negima!, although she's a little further down the family tree. She fulfills the harem-anime version of this trope by pulling out a book detailing her ancestry to deliberately (and successfully) spark total mayhem among Negi's Unwanted Harem.
The manga series Little Jumper features a high school student (Hiroki) who suddenly meets a girl (Chimari) who illegally time-traveled from the future to cure her ailing mother via genetic manipulation - and he is her (future) father. Two complications: 1) she hates her father (him), and 2) neither of them have any idea who her mother could (will?) be. A surprisingly widely agreed-on theory is that she could very well be her own future mother, which would effectively create both a Stable Time Loopand a decent amount of fan-discomfort.
In Tenchi Muyo!in Love, Tenchi Masaki himself goes back in time to rescue his parents from Kain.
Subverted in the second movie, Daughter of Darkness / Manatsu no Eve; Mayuka shows all the symptoms (and some of the characters just accept that she must be from the future, despite the bizarre (and scientifically impossible) means used to prevent Washu from identifying the mother through DNA analysis), but turns out to be an Artificial HumanLaser-Guided Tykebomb.
Urusei Yatsura uses a variation of this in chapter 11. Ataru tries to avoid arriving late to school by using time travel, but he ends up 12 years in the future and meets up with his son.
Nanami in Soul Link, the Half-Human Hybrid daughter of Nao and Shuuhei. As it turns out, she and she alone holds the key to defeating the Big Bad. Even though Nao and Shuuhei only had sex once (and both of them are still high school age), they have no problem taking responsibility as parents for Nanami, who apparently came into being even with Aries being a Building of Adventure.
An episode of Ojamajo Doremi's OAV had Doremi's granddaughter from the future travel to the present. note This, of course, raises the question of who Doremi hooks up with... and then, whose kid their kid hooks up with.
Nobita from Doraemon basically does Dane Cook's stand up joke from above in an early 90's episode to his parents, who had just had him as a baby, except with less twisted intentions. But hey, might as well warn them their kid's going to grow up into a (ten-year-old) loser, right? Though of course he might've cursed himself this way...
Sewachi, Nobita's great-great-whatever grandson, is the one who sent Doraemon to his ancestor in the first place. He also spoiled all of Nobita's failure future. Nobita's fate would have been so bad his descendant didn't care of any effect he causes from screwing destiny, since he believes he can be born nevertheless.
Aura of Mythic Quest is more an AI daughter from another dimension who suddenly introduces herself to her "father," but she plays about the same role in her parents' relationship.
NSFW Manga Yomeiro Choice has three (and counting, up to four and a cybernetic assistant/daughter!) daughters from the future, each trying to get the protagonist to impregnate her mother so she doesn't cease to exist.
In Steins;Gate Suzuha is this to Daru although, neither know at first.
Rachel Summers (Phoenix/Marvel Girl) is this trope played absolutely straight: she's the daughter of Scott Summers and Jean Grey in the "Days of Future Past" timeline's future, who goes back in time and joins various X-Teams.
Cable is a variation on this. He's the son of Scott Summers and Madeline Pryor (a clone of Jean Grey). He was actually born in the present (now past), but was taken to the future by the Mother Askani (actually future-future Rachel, his half-sister/genetic full sister). No, not the future she came from, another further distant future. There he gets cloned and grows up, later coming back as Cable to a period not long after he was born (but before he was taken to the future). His clone Stryfe follows him back.
Note that, briefly, Cable and baby Nathan existed concurrently but never interacted.
Nate Grey (a.k.a. X-Man) looks like this, but is not from the future: he's from the present of an alternate timeline, where he was genetically engineered from Scott and Jean's genetic material and given a Plot-Relevant Age-Up. He eventually wound up in the main timeline.
If you've followed all of this, you may have noticed that Scott Summers and Jean Grey effectively have had four children running around even though Jean was never pregnant. Three of those children are genetically identical, despite it being ludicrously implausible that the genetically engineered Nate Grey would end up with exactly the same DNA as Cable, who was conceived naturally in a different universe.
Other X-Men future Summers kids not tied to both of the above parents: Cyclops had a daughter with Emma Frost, in the form of X-Factor's Ruby Summers.
Also in X-Factor, it is revealed that Shatterstar is the son of Dazzler and Longshot who had been raised in the future of another dimension. This had been hinted at many times almost from the moment Shatterstar was introduced.
Surprise, surprise! It's now confirmed that Shatterstar is Longshot's son, but also (due to time-travel whackery), that Shatterstar is Longshot's father!
Another alternate-universe twist on this trope from X-Continuity is Nocturne, Nightcrawler's daughter with the Scarlet Witch, of all people.
Minor case: Bishop of the X-Men is from the future, and turns out to be the grandson of minor character Gateway.
In Battle Of The Atom, Future Kitty is really Mystique and Wolverine's future son Raze, a mutant who inherited both of his parents' powers.
For a non-X-Men example in the Marvel Universe, this has also happened in Fantastic Four with Valeria Von Doom, daughter of Sue Richards and Doctor Doom (or Reed Richards, though she certainly thought Doom was her father). Like Rachel Summers, she's a creation of Chris Claremont, and they've even both used the Code Name "Marvel Girl" (though in all fairness, Rachel had yet to use that name at the time of Valeria's creation). Clearly, Claremont loves this trope.
Then, Hyperstorm came. Who is Hyperstorm? Child of Franklin Richards and Rachel Summers in the Days of the Future Past alternate future. Yes, The two families who did it most in the Marvel Universe are now mixed together!
Impulse, Bart Allen, was the The Flash's cousin from the future — and the grandson of Barry Allen, the greatest Flash of the DC Universe.
Also, Impulse's half-brother, Captain Boomerang Jr.
Another case of the lead being the child is the current Booster Gold series, in which his distant ancestors are recurring characters. Booster explicitly references Marty McFly at one point.
In addition to this, Rip Hunter, who's playing mentor to Booster, has been revealed as Booster's son. The mother remains a mystery thus far. He deliberately keeps his parentage a secret so that other time travelers can't Ret Gone him by targeting them.
In one Astro City plotline, several versions of Jack-In-The-Box's son from the future appear (The Box, The Jackson, and Jerome Johnson). They grew up without a father because, in their timelines, Jack-In-The-Box died before his son's birth. One turned out to be a bloodthirsty vigilante, another ended up totally insane, and the third, 'normal' one was clearly emotionally wounded. This convinces Jack-In-The-Box to hand off his identity to a younger protege and concentrate on his family.
Lara-Su, the daughter of Knuckles and Julie-Su from two different possible futures in Archie Comics' Sonic the Hedgehog:
The first version of Lara-Su to appear, also known by the alias "Jani-Ca", first showed up in the early 100's issues. She came from a Bad Future (a very bad future recently dubbed "Dark Mobius" by Word of God), and attempted to avert it by preventing Knuckles' assassination. Except, when she got back to her time, not only did she find out that she had gone back into the wrong timeline, but that her mother had lied to her to protect her - Knuckles hadn't died, he'd pulled a Face-Heel Turn and was responsible for that bad future.
The second version of Lara-Su was from the much nicer "Mobius: X Years Later" timeline. She was one of the few people not affected by the Cosmic Retcon and helped Future Sonic depose King Shadow, and a while after that became a member of the Future Freedom Fighters.note It should also be noted that this version of Lara-Su never went back in time - so she's not so much a Kid From The Future as she is a Future Kid.
Lyra is the daughter of The Incredible Hulk and (a possibly/possibly not) the parallel universe future Anti-Hero Thundra from a world where the male heroes of today are worshipped.
In Gold Digger, Brianna Digger's daughter Roquette came back in time to stop her mother from marrying the wrong person! ... only to discover Brianna was merely planning the wedding of some other person and Roquette's timeline was unthreatened. Oops?
In the Avatar: The Last Airbender fanfic Tea With Destiny, Iroh travels to the Spirit World following the death of his son and intends to stay there forever. His son, however, doesn't think that's a good idea and takes him to visit with a very wise old man who turns out to be future!Zuko (Iroh isn't aware of this, as Zuko is currently ten years old in the real world). Future!Zuko advises Iroh to go back to the mortal world and be his mentor, because he's really going to need it.
Codename: Kids Next Door has inspired many fanfics that use this trope, such as this example. These fanfics tend to involve future KND Operatives meeting the present-day KND via time travel, or the present-day KND time-traveling and meeting future KND Operatives.
My Little Pony Fanfic Hands by Andrew Joshua Talon has an unresolved Love Triangle between a human, Fluttershy and Twilight Sparkle. In the Time Travel Episode after those three agree that Stable Time Loops are useless and cause only problems they get back to discussing how to resolve their Love Triangle. Seconds later two half human hybrids colored like Twilight Sparkle AND Fluttershy respectively arrive via Time Travel to tell their parents to just get a move on. They are actually Princess Luna and Pinkie Pie who traveled back from later that day to prank them.
The Harry Potter fanfic Far From Home and All Alone uses this trope with Remus Lupin, his future son Teddy and Harry's future daughter Lily. The two are sent to the past while Teddy is suposed to protecting Lily and instead gets in the middle of some dark wizards' nefarious schemes. Remus does not learn Teddy is his son until the end though.
In Twist Of Fate, the time-traveler Moses declares that Gunha Sogiita is Touma Kamijou and Misaki Shokuhou's son from the future who was brought into the present. The incredibly shocked and embarrassed Touma and Misaki suspect Moses was just messing with them, especially since Moses was snickering when he said it, but the incredibly gullible Gunha immediately believes it. Touma and Misaki are essentially forced to take responsibility for Gunha, even though they are roughly the same age, even going to a parent-teacher conference for him. It helps that they are much more mature than him. On the other hand, the girls in Touma's harem are not pleased that this means Misaki won.
Wilbur Robinson from the film Meet the Robinsons. It wasn't really the plan, but his actions do end up connecting Lewis with his family.
In the movie Back to the Future, Marty McFly is the kid from the future. He's also the main character and accidentally nearly prevents his own parents from getting together in the first place.
And in the sequel, Marty travels back to 1955 again.
And in the second sequel, Marty travels even further into the past and meets his ancestors, thus making him a Great-Great-Grandkid from the Future.
The 2011 film, Enter Nowhere has a child from the future, grandchild from the future, and a great-grandchild from the future. Tom is Jody's son, Jody is Samantha's daughter, and Samantha is Hans's daughter.
Alba from The Time Traveler's Wife (approximately—she appears after Henry and Clare are married but when they think they can't have kids, and Henry comes forward in time to see her about as much as she goes back to see him).
In one of the final scenes in the book, Alba visits Henry before he meets Clare. Even after she says she was looking for her father but was apparently too early, he still fails to understand who she is.
Done weirdly in the Doctor WhoEighth Doctor Adventures novel Father Time. Neither the Doctor nor his Kid from the Future, Miranda, knows that he's her biological father, despite the fact they look decidedly alike (when she grows up, they're even about the same height) and she's the only other member of his species he remembers meeting. He adopts her and raises her like his own, not realizing that she actually is. (Confusing things further, if Miranda's father is a future version of the Doctor [the books are only implicit on this point], then it's almost certainly a future that never actually happened; and was unlikely to happen even by the time of Father Time).
In Bones of the Earth, some time-traveling paleontologists get stranded in the Mesozoic for months. Once rescued, they're welcomed home by hordes of media and friends from many different times ... including an adult version of the baby one of their group gave birth to in the Mesozoic. He doesn't save them, but he gets to hold his infant self.
This trope is central to The Glass Ruins, where the main character is sent into the past to prevent his mother who is pregnant with him from having an abortion.
Live Action TV
Wyatt and Chris on Charmed, the children of Piper and Leo. Future Wyatt only shows up after Baby Wyatt has been born, but Future Chris preceded Baby Chris and his identity was an object of speculation.
Chris almost causes himself not to exist the same way Marty McFly did, by breaking up his parents. Except he did it on purpose, apparently not ever bothering to do the math and figure out when he was conceived. This was due to Real Life Writes the Plot. Chris was always going to be their son, and that reveal had already happened, but Piper's actress got pregnant halfway through the season, while Chris was deliberately keeping Leo away so Leo wouldn't figure out who Chris was and what he was doing. So the writers had to scrabble to get in a one-night Leo-Piper hookup arranged by Chris to explain the pregnancy, and Chris looks like a complete idiot for almost erasing himself from existence.
Clarification as to the original plan for Chris' origin: Chris was supposed to be Phoebe and Cole's son from the future, that was supposed to give Phoebe a reason to have hope for her then unfortunate luck in romance. It makes sense given his original actions earlier in the season - he had strong connections to demons and moved around in the underworld to access magic that would protect his identity from the Charmed Ones. The pressure was really on to identify whose kid he was after Holly Marie Combs became pregnant though, and it's incredibly fortunate that the series hadn't revealed Chris' origins beforehand for the writers' sake
Alexander Rojenko does this in an episode of Star Trek: The Next Generation. Due to having grown up to be a pacifist and diplomat, his perceived weakness lead to him nearly being assassinated by political rivals, with Worf Taking the Bullet. He travelled back to convince his younger self to become a warrior as his father had wanted, but when this plan fails, he attempts to kill his younger self to ensure that future never came to be. Worf luckily convinces him that the future is not set in stone and even if he pursues the path of peace, it is something he would be proud of.
Two other Star Trek episodes, namely the Deep Space Nine episode "Childen of Time" and the Enterprise episode "E2", had a variant of this trope, in which the descendants of the crew (of the Defiant and the NX-01 respectively) ended up in the present due to the ship's imminent travel into the past, with no way back. In both episodes, the time travel eventually gets prevented, but not without paying the high price of the "future" children's existence.
And both Sam and Dean in the episode "The Song Remains the Same".
Wataru becomes one to Otoya in Kamen Rider Kiva when he decides to travel back in time both in-series and in-movie. Ironically, he does so because he's in despair at accidentally killing his love interest Mio, so he tries to convince Otoya and Mayanot to have him. In the end, both convince him to choose to live. Given the strong Generation Xerox Kiva has, Wataru's son from 22 years in the future appears in the finale, along with Kivat the 4th, who gives him the power to become New Kiva.
Kamen Rider Den-O is a natural candidate for this, given its plot. The series proper has Hana, who as the child of Yuto and Airi, is Ryotaro's future niece, which makes all that Ship Tease turn a little sour in retrospect.... The MovieFinal Countdown features Kotaro, Ryotaro's grandson, who is also New Den-O.
Power Rangers Ninja Storm - Cam's journey to become Sixth Ranger involves using a magic scroll to travel back in time. He witnesses his parents' first meeting (his mom kicking his dad's ass in front of their entire Ninja School), and "inherits" his morpher from her before returning to the present.
Claire Bennet plays this role in a season 3 episode of Heroes, as does Hiro Nakamura.
On LOST, time travel begins playing a role in the fifth season. After being transported back to the 1970s:
Miles interacts with his parents and sees himself as an infant. Miles wishes to have no relationship with his father because he allegedly abandoned Miles and his mother. Through predestination paradox, it is revealed Miles' friend Daniel Faraday was responsible for this: Miles' father didn't abandon his son, he forcibly made them leave the island to survive a catastrophic incident that would happen hours later, having been told of this by Daniel.
Daniel himself believes he can stop said incident by finding his mother, Eloise Hawking, a member of the Others, then having her help him detonate a hydrogen bomb that he told her to bury when he time travelled to 1954. However, when he arrives at camp, she shoots him in the back when he holds up Richard Alpert, and as he dies he tells her he is her son. She is forced to live the rest of her life knowing her son will grow up, go back in time, and be shot dead by her unknowing past self.
And then she sends him to the Island in the first place, knowing too well what's going to happen. It is all really tragic, but she must have really disliked time paradoxes to allow all this to happen.
She didn't "allow" anything to happen. "Whatever happened, happened". As she told Desmond, any attempt to change what is fated will be futile, as it will happen anyway.
The ending of the last ep of Lois and Clark was a setup for this trope.
Even though the same episode had DNA testing establish that Clark could never have a child with a human woman. Of course, it's not entirely unlikely that an advanced species like the Kryptonians could have devised a way to make such a pairing work.
River Song, first introduced to Tenth Doctor and killed off in 2008, turns out to be the daughter of Eleventh Doctor companions Amy and Rory, introduced in 2010. Her example is among the most extreme on this page — thanks to the Timey-Wimey BallandTime Lord Regeneration, she actually spends her entire teenage years growing alongside her parents as their contemporary Black Best Friend, even playing a role in hooking them together. She also visited her parents' wedding and later married the Really 700 Years Old Doctor herself, making her 20+something old parents his in-laws.
An earlier episode, "Father's Day", has companion Rose Tyler meet her mother, father, and infant self.
Jackie: Her dad? How are you her dad? How old were you, twelve? Pete: Jacks - listen. This is Rose. Jackie: Rose? How sick is that? You give my daughter a second hand name? How many are there? Do you call them ALL Rose? Pete: Oh, for God's sake, look! It's the SAME Rose!
In the episode "Hide", the Doctor meets a scientist and a psychic investigating a haunting, and discovers the "ghost" to actually be a time traveler stuck in a pocket universe. After they rescue the girl, the Doctor reveals the time traveler to be one of the scientist and psychic's descendants, even though they weren't even technically a couple yet — they had just finally begun to recognize the mutual UST.
In the final season of Goodnight Sweetheart, Gary (who regularly time-travels back to World War II, and maintains a second life there) is taken aback to meet his Kid In The Present.
In the detailed character biographies of Kitsune: Of Foxes and Fools it's stated that Akomachi's daughters Sharmarali and April, grandkits Akira and Cori, and apprentice Aoki all came back in time to see what she was like before her ascension.
Trinity from Boktai 3, according to Word of God, is a distant descendant of Django. He does one good thing (Break the seal that trapped Django, whose absence led to the Bad Future to begin with) before comfortably settling into his position as The Load.
Tales of Destiny 2 has Kyle, the protagonist, meeting his parents in the past. Stahn even jokes that he'll name his son after Kyle. He never reveals that he's their son, though.
Arguably, Silver from Sonic the Hedgehog. It's implied that he's the descendant of either Sonic or Shadow, but it's never specified which.
Although Sonic and the Black Knight is a spin-off whose place in canon is disputable (although Generationsdoes distinctly, if not offhandedly mention the events of its direct predecessor, Sonic and the Secret Rings...), it should be noted that Shadow is portrayed there as Sir Lancelot. Silver, although a secret character with no plot importance, also appears in that game as Sir Galahad, Lancelot's son. Make of that what you will.
The main plot of the best-forgotten game Time Diver.
Interestingly, Beatrice is barefly mentioned in Space Quest 6, and Roger is trying to get together with another woman, apparently forgetting the time loop. It's possible, of course, that he simply wants to have a fling with Stellar, while Bea is busy elsewhere. The preview for Space Quest 7 (which was never made) once again has Roger trying to save Beatrice.
She's also implied to be Ayla's Descendant From The Future.
In the Ambitions expansion pack for The Sims 3, it is possible to end up with one of these when using the time machine.
Inazuma Eleven 3: the Orge features Endou Kanon, a kid from the future who try to stop an evil organization that tries to get rid of Kanon's great great grandfather, Endou Mamoru, and his Japanese international soccer team.
It's even funnier: regardless if Vivio is in her Adult Mode or not, Nanoha acts like a mother to her like she will do in the next 9 to 13 years.
Achron has a partial example. It's possible for a factory (parent) to produce a unit (child) which then gets sent back to before it was built (born) to defend the factory.
All over the place in Fire Emblem Awakening. "Marth" reveals her true identity as the grown-up version of Chrom's daughter Lucina. After this reveal, when a male and female campaign character reach S support level, you can recruit their kid in a side chapter. There are a total of 13 future children; at least one of them will be yours. To make things even more ridiculous, your future kid can end up as the future kid of one of the other 12 future kids if you marry one of them.
Petta from the PSP remake of Makai Kingdom is the daughter of Zetta (the Protagonist and self-proclaimed "Most Badass Freakin' Overlord in the Cosmos",) having traveled from the future... Or so she claims. Surprisingly, she is indeed the daughter of Zetta and Salome; the reason she came from the future is because the prophecy that set the game's plot in motion still persists in her era, so she went back in time to prevent it.
Ele of Star Gladiator. She's a cute girl from the future who happens to be the daughter of Hayato and June.
In Narbonic, Dave and Helen's child abuses her parents' Universe-consuming time machine ("We siphon it from universes where they probably don't want to exist as much") to spy on her parents before they got married — and arguably creates a Stable Time Loop by convincing Dave to get back with Helen, a decision without which she wouldn't have been conceived.
Similarly, in Umlaut House, Rhonda goes into the past to settle an argument with Pierce, who follows her to keep her from meddling in the past (as it happens, he shouldn't have bothered).
We later meet him in Act 6, where it turns out Jade is his grandmother - except it's an Alternate Universe version of Jade. And J's counterpart in the original universe was Jade's grandfather... who was also her genetic father.
Arthur, King of Time and Space's space arc has a variation: Morgan has been brought forward in time to serve as Merlin's apprentice. While there, she and Arthur conceive a child, not realizing that they're half-siblings. When Merlin finds out, he returns Morgan to the past and she gives birth to Mordred... who in the present day is already serving aboard the Excalibur and doesn't know any of this. Also, Morgan met Squire Mordred while on the Excalibur, and was so imprssed by his ambition, she named her son after him.
A second, more straightforward example: Nimue, also a time traveler, brings Galahad from the future to meet Lancelot.
In the comic Transypoo! Acey's daughter from the future, Jo Smit, goes back in time, seemingly, to provide futuristic armor to the main cast, and possibly just to have fun.
Brady "Honey" Smith from Sailor Sun is a parody of this trope, and specifically Chibi-Usa.
Cassandra Cain from Cass Cult is on fairly good terms with the Legion of Cass Daughters, which includes her daughters from every possible timeline.
In Red Panda Adventures, The Red Squirrel reveals in her first appearance that The Flying Squirrel was her great-grandmother, but it's not until later that she also confirms that The Red Panda was her great-grandfather, since she didn't want to affect the timeline by interfering in the Will They or Won't They?.
In We Are Our Avatars: A portal created by Damara Megido enabled the future kids to visit the past versions of their parents.
Warhawk in the animated version of Justice League was Green Lantern (John Stewart) and Hawkgirl's Kid From The Future—which came as a surprise because they had stopped dating quite some time before traveling to the future and running into him.
Technically there was two such cases in that episode, as a later episode tells us that Terry McGinnis (Batman II) is Batman's biological son created by Amanda Waller.
These two are actually inversions, given that, as mentioned above, their parent came to them. This actually causes John to attempt a Screw Destiny by not getting back together with Hawkgirl over the course of the series just so he doesn't feel pressured to do so just by Warhawk's existence. Word of God says that's okay, given that Warhawk is still only in his twenties by the Beyond time period, which is still a good forty years off.
In Time Warp Trio, the original trio of Joe, Sam and Fred sometimes cross paths with their great-granddaughters from the future: Jodie, Samantha and Freddi.
Jake becomes this in one episode of American Dragon Jake Long when he travels back to 1986 and accidentally causes his parents to split up. He then has to strive to get them back together in order to ensure his own birth.
Destructicus, son of Hector and Dr. Ghastly, from Evil Con Carne. This raises questions on how this happned however as Hector is a brain (and stomach) in a Jar attached to a circus bear....
Danny himself does this when he travels back in time and prevents the accident that gave Vlad ghost powers. His mother ends up marrying Vlad instead, and they have no children. Danny has to convince her to help him fix things so he can go back to his own timeline.
Played With on Phineas and Ferb, where they go to the future and meet their sister Candace's kids. We don't actually find out much about Phineas and Ferb themselves, including if either of them has children. Though it is implied that oneof them marries Isabella.
In one Halloween Episode of The Simpsons, Bart travels back in time and meets Homer in high school, introducing himself as "the unwanted son from the future who kills all your fun." Homer starts strangling him at the very moment he first meets Marge, and she is so disgusted that she never marries him, and Bart becomes the son of Marge and Artie Ziff.
In one episode, some villains from the future travel to the present to assist the present villains. One of them addresses Dr. Blight as her ancestor. Dr. Blight says that can't be possible because she doesn't have any children and doesn't plan on having any. The woman glances significantly between Blight and Looten Plunder and chuckles, saying she will. Blight and Plunder get nervous and disgusted. It becomes a moot point because the changes done to the timeline end up causing the future villains to suffer a Ret Gone.
In a different episode, Dr. Blight's daughter Betsi comes to the present. To everybody's shock, she is a good guy.