So I think I'll be six for ever and ever."
As you know, Growing Up Sucks. Some children, however, have found a way to halt their aging at childhood via Applied Phlebotinum or some supernatural means. Most of the time they'll have the mind, emotional maturity, and/or sensibilities of a child as well as a prepubescent body; adults in children's bodies are more likely to find it inconvenient or downright sucky, which is the Sub-Trope, Not Growing Up Sucks.
Note that this must happen in-universe. If characters in a long runner series stay forever in a given age simply to keep the setting the way it is (like The Simpsons all being the same age for over 30 years), that's Comic-Book Time.
- A bit of a supernatural occurrence happens in Spirited Away, where it's implied that Yubaba's overly coddling of her son Boh made him stay physically and mentally a baby.
- One episode of Cowboy Bebop features a Creepy Child. Supposedly, whatever stopped his aging also made him bullet- and explosion-proof.
- In Fate/Zero, Ilya, Kiritsugu's daughter with Irisviel von Einzbern, is absolutely tiny despite being eight. She's actually growing more than most homunculi of her type do but he thinks there's a 90% chance she'll stop growing before hitting puberty. In the next Grail War ten years later she's slightly older than Shirou yet is still the game's Token Mini-Moe.
- The Trigun anime reinterpreted Zazie the Beast this way, apparently. Since the eternally-respawning humanoid avatar of the sand-worms' group intelligence would have been too complicated to deal with in one episode. Hell, the manga doesn't really deal with it completely.
- Kaori Yuki's Cain Saga manga series features an extremely sympathetically-presented member of the Nebulous Evil Organization, Cassian, a middle-aged man in the body of a prepubescent boy, formerly employed as a knife-thrower in a circus. He joined the organization because they have weird, futuristic occult-medical hybrid technology in development which might give him some way to get an adult body. He's assigned to be the primary minion of a high-up member of the organization, Doctor Jizabel Disraeli, who's around twenty and as we get his backstory, increasingly pitiful. Dealt with well in that Cassian, even though all visual cues are against it, sees Disraeli as a kid. Cassian is fatally wounded about as soon as his pseudo-paternal attachment to Disraeli is properly developed, and Jizabel transplants his brain into the head of a fellow villain they both hate who was recently thwarted by hubris and idiocy. (And the hero, in one of the hero's few success stories.) Cassian goes on the lam, and reappears as a handy plot device toward the end of the series' climax. Disraeli eventually dies in his arms, lamenting the fact that he spent all this time trying to please the wrong father, Alexis, the twisted Man Behind the Man, when he should have been looking up to Cassian. Cassian has many levels in awesome.
- Eriol Hiiragizawa in Cardcaptor Sakura is mostly this with a bit of Not Growing Up Sucks. He specifically chose to halt his aging, but while he looks like a child, he's mentally an adult. He doesn't have any angst over his age dissonance shown, but since he only stopped his aging so he could blend in with Sakura's classmates better, it would probably make his life after the series more complicated and restricted if he can't restart his aging.
- Akio, Anthy, and possibly Mikage from Revolutionary Girl Utena all have some form of this, with the former two are implied to have been at Ohtori Academy for centuries. At the very end of the series Anthy decides to leave by "graduating" as a metaphor for growing up.
- In Pokémon Adventures, despite the fact that it is well over three years old, X's baby Kangaskhan never grew nor left its mother's pouch, mirroring its trainer's Hikikomori lifestyle.
- In a completely unexpected move, Rebuild of Evangelion 3.0 has Shinji is woken up from stasis 14 years after the end of the previous film and confronted by a 28 year old Asuka who still looks very much like her 14 year old self plus an Eyepatch of Power. Asuka mentions that it happened because of the "Curse of Eva"; personality-wise, she's considerably less bratty and quite bitter. Mari also appears to be affected but Rei isn't, considering that it's not the same one Shinji knew.
- This is part of the reason Dr. Tenma abandoned Astro in Astro Boy. He created Astro Boy as a Replacement Goldfish for his deceased son Tobio however Astro, being a Robot Kid, cannot age. What makes this especially odd, is that Astro's "little sister" Uran, also a robot, actually did grow up! She went from being a short, chubby preschooler in her first appearance, to being able to impersonate Astro with a simple costume change, to the point where she looked more grown up than her "big brother", as a slender young woman in the later stories, complete with superfluous (though modest) artificial breasts (!). Tezuka also experimented with drawing Astro looking more like the teenage adventure heroes that were popular at the time, but apparently his readers didn't go for it. They didn't complain about Uran nearly as much, though. Then there's the Astro's Been Stolen story, where an attempt is made to give Astro an adult body, but it turns out to be a piece of junk that only has the same power level as his original despite being much bigger. The story ends with him musing that Growing Up Sucks and if you can avoid it you probably should.
- The cyborgs in Gunslinger Girl are implied to be physically stunted by their conditioning. They're preteen and teenage girls who have been given cybernetic implants and medicine to make them Child Soldiers. None of the first generation lived long enough to see if they could grow into adults.
- Another Osamu Tezuka example is in Black Jack with Pinoko, an Artificial Human created by Black Jack who has 18 and even more but her appearance still looks like in her 10s.
- Deconstructed in The Twelve Kingdoms. When kings are chosen to rule their nation they are granted immortality, along with their families. Princess Shoukei was 13 when her father became king, so she is locked at that age. However, her parents keep her sheltered and spoiled and do not allow her to grow up both physically and in maturity, so when her tyrannical father is overthrown decades later, she still looks and acts like a Royal Brat despite being chronologically in her forties. Learning to grow up and get past her stunted maturity is the major part of her Character Development.
- Hard Being Pure: Dr. Emilly is stuck at the appearance of a 10-year-old girl, and hates how she gets treated like a child even though she is mentally a 27-year-old.
- In The Powerpuff Girls' Dark Fic The Utonium Trials, the girls are permanently stuck looking five years old due to being Artificial Humans. They're nine years old (five chronologically) but still look five. Their young looks cause them to be bullied by their classmates and causes even worse problems once the government takes note of them.
- In Rainbow Brite and the War of Darkness, Rainbow and the other Color Kids are several million years old but have the bodies of little kids. They're at least more mature than normal children.
- Lost Storms: Stormy's Forgotten Past: In Rainbow Land, people don't age. Stormy has hardly grown an inch since she was six. She's currently over seven hundred.
- Tiny Sapient Ungulates:
- Spike's growth is stunted and he is stuck in his infant size due to his incomplete diet.
- The changelings' "evil" forms are interpreted as their juvenile form, and Chrysalis prevented them from reaching adulthood.
- The Infinite Loops: Children can become loopers. Depending on how long the their baseline loop lasts, this might mean they are stuck as children for a long time. In The MLP Loops, Spike has an extra problem when he gets married. He and his wife are thousands of years old and he has age-shifting magic to easily transform into a form more appropriate for his wife, but as far as non-loopers are concerned he's still a child, and certainly not of legal age to marry. With the exception of lucky variant loops where he's older, they have to keep their relationship secret.
- The imaginary friends in Drop Dead Fred don't grow up. It is implied that those who do not grow out of needing their imaginary friends are ultimately prescribed pills that hurt or kill the imaginary friends.
- In A Beautiful Mind, Dr. Nash figures out that his hallucinations are exactly that, when he realizes that Marcee has not aged a day in the years that he has "known" her.
- The Trope Namer is Peter Pan, or The Boy Who Never Grew Up, which has the Lost Boys as well as Peter Pan himself. Peter Pan is a young boy who refuses to age. He and his group of Lost Boys live on Neverland, a magical island where no kid has to grow up. The novel actually plays with this. The Lost Boys arrive as infants and age into children. Peter is also known to weed out (which may-or-may-not mean he kills them) any Lost Boys who age.
- The story Child of All Ages is about a child who regularly drinks a potion which keeps her young (it also lets her live for hundreds of years, so she isn't about to stop, even though there are many disadvantages to being a kid).
- There's a SF short story called "Start the Clock" that features this. Basically, one day everyone on Earth stops aging, and stays in whatever "state" they were at the time... little kids have it the best, in a way, because their brains stay in the "good at learning" state... and at the point in time the story's set, they've gotten the same rights as adults (they can hold jobs and live on their own and such). Anyone going through puberty got the worst deal, since it just keeps going, deforming them and giving them health problems. Infants tend to get cybernetics, and are scary and powerful.
- Although by the time the story is set treatments to allow people to continue to age have been developed.
- Oskar, the protagonist of Günter Grass's novel The Tin Drum, deliberately stunts his growth at age three, by hurling himself down the stairs, so that he can avoid being part of the horrific adult world around him. He attempts to shield himself further from adult horrors by drowning them out with his titular drum. In the end, however, a blow to the head ages him instantly.
- Harlan Ellison's short story "Jeffty is Five" is about a kid who is always five. Not only that, but he is also seemingly an unconscious Reality Warper; he continually gets to see new movies starring actors who've been dead for years, new episodes of radio shows that have been off the air for decades, and read new issues of comics that don't exist anymore. This leads the narrating character, who's highly nostalgic for his boyhood days, to spend a lot of time with him... until, as usually happens in an Ellison story, it all goes horribly awry.
- The Gull of "The Age of Five" trilogy by Trudi Canavan is sort of an example of this trope. Whilst his body is that of a seven or eight year old child, he has the knowledge and maturity that he has acquired over thousands of years of life (he's also the oldest of the surviving immortals, a fact which, when revealed, causes his fellow immortals to lapse into a thoughtful silence as they wonder just how old he is.)
- Just like in the original Disney adaptation, Peter Pan doesn't age in Disney Fairies. In the first book however, Mother Dove starts to slowly die and all the magical elements of Neverland begin dying with her. Peter begins growing and losing all his baby teeth. When Mother Dove is saved, Peter de-ages back to his original age.
- Invoked by Pippi Longstocking, who, in the end of the last novel, takes a pill together with Tommy and Annika, which together with a rhyme, allegedly stops aging.
- Claudia from Interview with the Vampire is a literal case of a little girl who is Really 700 Years Old. She was a five year-old girl who was bitten by Lestat to save her from the plague and being part of Lestat's "family". Ultimately, the denial of adulthood drives her to insanity.
- Invoked in the Land of Oz books. A person can only age in Oz if they so wish to. Thus, Dorothy can stay a Kid Hero forever if she wants. In one book she is sent back to America and turns from a 5-12 year old to a middle aged woman.
- Defied in the Greg Egan story "Singleton": To help their Artificial Intelligence daughter mature, the main characters start her out in an infant-like chassis and transfer her core into progressively older bodies to parallel human development.
- In-Universe in Mort, where Ysabell has been kept at 16 years old for 35 years because of living in Death's domain as his adopted daughter, because of Death's mistaken belief that that would be the easiest option. She is allowed to age normally when she leaves with Mort back into the real world.
- Twilight: Vampirism halts someone's development, locking them into their current state forever, but enhancing their natural characteristics. If it happens to young children, they become utterly adorable, causing people to fall in love with them at first sight, but they never learn self-control; they could slaughter entire villages whenever they became thirsty, and they would never grow out of it. The Volturi studied them for a while, but eventually decided that there was nothing to be done, executing them all and making the creation of more a capital crime.
- The first episode of Eerie, Indiana involves two identical twins called Bert and Ernie who never got older than twelve and had to repeat seventh grade for thirty years because their mother locked them inside age-retarding Foreverware each night. As they state in unison, "It's a living hell". The main character pops their Foreverware open at the end of the episode, and they in turn do it to their mother, who used the same trick to stay youthful; the next morning, the twins are happily in their forties, and their mother is now an old woman.
- Tom Baker's incarnation of the Doctor on Doctor Who lampshades this at the end of the episode "Robot" when Sarah Jane says he's acting childish:
Doctor: Well, of course I am! There's no point in being grown up if you can't be childish sometimes.
- The Star Trek: The Original Series episode "Miri" revolves around a planet where an anti-aging drug led to a society of 300-year-old children, and no adults. (Although technically the children are growing up, just incredibly slowly.)
- Heather Dale's "Changeling Child" is a Changeling Tale about a woman who couldn't have children of her own. She bargained for The Fair Folk to give her a baby but, being Literal-Minded, the fairies give her a baby, not a normal child who can age:
How their home was joyful with a son to call their own
But soon, they saw the years that passed would never make him grow
- Werewolf: The Apocalypse: One of the character templates in the White Howler tribebook is a Metis woman whose deformity leaves her human form similar to a prepubescent girl (and her natural War Form no larger than an ordinary human adult). She serves as a spy and infiltrator.
- Juvenat treatments in Warhammer 40,000 allow a person to fix themselves at the age they want to look like (some people go for eternal youth, others in positions of authority go for The Patriarch look) in addition to prolonging their lives by a century or two.
- Breath of Fire IV has an entire town of these; the town of Chek is entirely populated by what appear to be kids but are actually people in their teens on up to elderly people. It's also a town entirely populated by summoners and shamans, and it's outright stated in the game that it's their proximity to the summoning temple for the gods in that universe that keeps them young.
- Seere from Drakengard, who sacrificed his ability to age as part of his Pact with his Golem. It is more apparent in the sequel which takes place eighteen years later.
- In Grand Theft Auto: Vice City, there's a radio advertisement for the fictional sitcom Just the Five Of Us, in which one character is a 42-year-old investment banker with a rare disease that makes him look 10 years old.
- Rika from Higurashi: When They Cry is stuck in a "Groundhog Day" Loop where she is the only one who remembers each universe. She is between nine and thirteen but has been stuck in the cycle for hundreds of years.
- Fecto Forgo, the Big Bad of Kirby and the Forgotten Land, is a variation. After separating from Elfilin, the embodiment of their compassionate side, Fecto Forgo reverted to their immature larval form and lost the ability to survive outside of the Eternal Capsule.
- The Kokiri from The Legend of Zelda: Ocarina of Time are given life by the Great Deku Tree and automatically stop aging at around 10. But as seen in The Legend of Zelda: The Wind Waker, they can have their form changed by the Deku Tree in order to protect them (in this case, the great flood) so the tree may have given them this attribute.
- Magical Girl Lyrical Nanoha A's Portable : The Gears of Destiny has Yuri Eberwein, the formerly human Unbreakable Darkness who achieved Complete Immortality when she became what she is now. The Sound Stages set after the game mention that, now that she could control her unlimited powers, she could let herself grow up as normal again.
- Touhou Project has an interesting case of this trope being fuelled by Immortal Immaturity: according to Word of God, resident vampire sisters Remilia and Flandre Scarlet have forfeited their growth and maturity in exchange for eternal life. In other words, the sisters have the appearance and mentality of ten-year-old children because one of them is a Royal Brat, and the other confined herself to their basement for 500 years, which stunted her mental and emotional growth.
- Xenosaga: Rubedo, who's an artificially created human with the power to slow down cellular growth, stopped his own aging at around age 12. This means while he's technically older than Guignan, he presents himself as Guignan's son, Guignan Jr. or just plain Jr.
- Philippe from Achewood also seems like he will always be five, especially if this strip is canon...
- Unsounded: All Senet Beasts are Time Abysses from the First World, created before the Gods even came up with the concept of growing up and aging. The waterwomen appear to be of all ages, but the baby ones are as ageless and unchanging as the others.
Minnow: Don't let them take advantage of you. They've been babies longer than the moon's been round.
- Some characters in Tower of God play adult roles in spite of looking like children or teenagers. Anaak Jahad is an obvious example — she's implied not to be half as young as she looks (which is something like barely in puberty), is one of the most powerful fighters among the Regulars, and doesn't much change in terms of looks during a Time Skip of years. It's revealed in the wiki that some people in the Tower just don't physically grow up. It's also said that they are considered as having childish personalities as well, though how true this is isn't clear. Anaak, for example, gives little clue: does her emotional coldness reflect a secretly damaged child or secretly damaged adult? The wiki also reveals that a character with a permanently childish appearance (in this case, Eurasia Blossom) can be in a relationship and have a child with an adult-looking adult (Po Bidau Gustang).
- Whateley Universe: Generator is 14-15, but has looked like she's 11 from since she was that actual age.
- The imaginary friends from Foster's Home for Imaginary Friends are real, and childlike, but never grow up, which becomes tragic when their creators grow out of them and eventually abandon them. Some, however, are likely needed for life, such as an imaginary friend created to help his blind creator. Other few get the luxury to be passed down to their creators' children.
- Batman: The Animated Series: Actress Mary Louise Dahl suffered from a very rare disease that prevented her from physically aging past the age of about 6 or so. She was a sitcom star for a while playing a little girl named Baby Doll. Eventually, she quit and tried to become a serious actress with less than no success. After a series of failures she resorted to kidnapping her old castmates in an attempt to relive her glory years and drawing the attention of Batman.
- In Young Justice, Superboy still looks the same after a five year Time Skip. One of the side effects of the cloning process that created him is that he will always look sixteen. He still ages internally, so he's not immortal.
- Codename: Kids Next Door: An ugly girl at Gallagar Elementary has been secretly using the Fountain of Youth hidden in a cave underneath the school to sustain her youth and has managed to stay a child for thousands of years.
- Steven Universe: "Steven's Birthday" reveals that Steven seems to have stopped aging at 8 years old. However, the ends hints he is growing old somewhat, and earlier episode showed his body's maturity depends on his mental state. By two years after the original series, he has grown noticeably older.
- Timmy from The Fairly Oddparents seemed to be stuck in the common trap of cartoon children never aging. The episode "Timmy's Secret Wish" deconstructed this. It turns out that Timmy actually wished that nobody could ever age. Real-world time the show was under ten years old, but in-series 50 years had passed (meaning the show takes place in the 2050s). At the end of the episode Timmy reverses the wish so that everyone can age again.
- Played for Laughs in a non-canon The Simpsons episode where they are depicted as Animated Actors. In order to keep Bart and Lisa kids forever, Homer gives them anti-aging hormones.
- It's implied that the Ambiguously Human Color Kids from Rainbow Brite are much older than they seem. Rainbow used to be a normal human but she's way smaller than normal now and also seems to not age.
- There was Brooke Greenberg, who had a mysterious medical condition that had caused her mind and body to remain in infancy for 17 years before she died in 2013 (with some anomalies, such as her bone age being around that of a ten-year-old). There's no obvious supernatural involvement, although her first five years or so of life were full of medical catastrophes that spontaneously resolved without leaving any damage (for example, a brain tumor that spontaneously disappeared). This article has a video that shows her at twelve years old, looking much like a six-month-old infant.
- Though given that her telomeres were shorter than a normal child her age, Brooke could've actually aged faster than normal - even though she didn't grow up. It didn't happen.
- Then there are people who have Hypopituitarism, making them look like pre-teens/middle-schoolers long into adulthood. Comedian Andy Milonakis is a famous example.