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* ''WesternAnimation/AdventureTime''
** The Earl of Lemongrab is an interesting version of this. Physically he's eighteen at the youngest, but because he was born in a laboratory, he's only about one year old chronologically. He acts like a bratty little kid trapped inside the body of an adult, mainly because he IS a very young brat who happens to be an adult, too.
*** He and his clone/[[AmbiguouslyGay boyfriend]] have kids together... and they're STILL immature manchildren.
** Jake also very much resembles this at times, to the point where one wonders if he's an English Bulldog, as he closely resembles physically, or if he's a [[BigFriendlyDog Golden Retriever]].
* Richard Watterson from ''WesternAnimation/TheAmazingWorldOfGumball''. If anything, he's even ''more'' immature than his own offspring.
* Sterling Archer in ''{{Archer}}'', despite being a world-class secret agent, it also a brainless and immature MommasBoy who is often more interested in things like pirate lacrosse or ''Film/{{Aliens}}''-style space robots than the safety of his companions.
* WesternAnimation/BatmanBeyondReturnOfTheJoker: SelfDemonstrating/TheJoker points out that for all the fear he invokes being TheCowl, Batman is really this trope:
--> "I must admit, it's sadly anti-climactic. Behind all the sturm und batarangs, you're just a little boy in a playsuit, crying for mommy and daddy! It'd be funny if it weren't so pathetic... Oh, what the heck, I'll laugh anyway! ''([[LaughingMad Mad Laughter]])''"
** Years later the second Batman, Terry [=McGinnis=], throws the Joker's insults right back at him by pointing out that the Joker himself is also this trope as his fixation with the original Batman was childishly pathetic and, once you take away all the garish make up and fancy props, the Joker was really nothing more than a stupid, overgrown kid trying to make people laugh at a joke that wasn't all that funny to begin with, angering the Clown Prince of Crime greatly.
* Several characters in ''WesternAnimation/BatmanTheBraveAndTheBold,'' most notably ComicBook/PlasticMan.
* The animated version of ''WesternAnimation/{{Beetlejuice}}''. The majority of the inhabitants of the Neitherworld are fairly mature. Beetlejuice most likely expired in his late 30s, but he's mentally about eight, and a childish prankster who hangs around with a twelve-year-old Lydia in an IntergenerationalFriendship.
* TheEeyore of ChalkZone, Mr. Wilter. Lampshaded in his EvilTeacher roles.
* Dexter's Dad from ''WesternAnimation/DextersLaboratory''.
* ''WesternAnimation/TheFairlyOddparents'': Timmy Turner will apparently become this in the future, according to his show's LiveActionAdaptation, as pictured above.
** Every adult in Dimmsdale is this.
** Cosmo, despite being thousands of years old he acts immature at times, and still wears diapers.
* Peter Griffin from ''WesternAnimation/FamilyGuy'' wavers between this and PsychopathicManchild.
* While he technically isn't this yet, Debbie Douglas expresses hope that her son, Duncan becomes one of these in ''WesternAnimation/{{Freakazoid}}'' because he's not exactly opposed to it.
-->'''Debbie:''' "You'll be a big strong man-child, still lifting weights in your room when you're forty!"
-->'''Duncan:''' "Cool! That way I can ''really'' buff up, and save some money!"
* Philip J. Fry from ''WesternAnimation/{{Futurama}}'' has since the beginning of the series been the epitome of Generation X (or Y perhaps): A big 20-something man-child. He plays video games, watches TV, drinks soda by the gallon, does anything if he's dared to do it, and has no ambition in life except for one... love. He's that flat mate that you knew who just can't seem to truly grow up (...and is often fully aware of it. Refer to his one ambition for why this is a source of gloom for him often), but at least he's cool to hang out with.
** The new season reveals that Fry is 35. Adult Child, ho!
** Actually, he might be as old as 31 since in one episode, he and the Planet Express crew [[spoiler: were affected with chronotons that reversed their aging and then they negated the effects by going into the Fountain of Aging.]] And they, sans the Professor were [[spoiler: reborn in the series's revival.]]
** [[spoiler: Fry is his own grandpa]] and that caused genetic damage, which caused his brain to develop abnormally.
** Also, 'cause of that whole [[spoiler:Lars is an alternate Fry plot point]] in [[TheMovie Bender's Big Score]], this puts Fry's age at just older than '''''2037 years old'''''.
** Also, Zapp Brannigan, though that's more disturbing as he is in a position of power, with the authority to get people killed in mass amounts. Which he fully utilizes to do just that.
* ''WesternAnimation/GravityFalls'' character Soos is described as this by the show's promotional material and website. Given that he's a semi-CloudCuckoolander who's OneOfTheKids, this is a given.
** Even said so by Grunkle Stan in the season 1 finale, saying "you're a good man...child, Soos".
* Glickenstein and King Malbert from ''WesternAnimation/{{Igor}}''.
* Lucius from ''WesternAnimation/JimmyTwoShoes''.
* The titular character of ''WesternAnimation/JohnnyBravo''. He's in his mid to late 20s, still lives with his mother, throws temper tantrums when he doesn't get what he wants, spends much of his time playing with toys, has a lot of childlike interests, and he sleeps with a teddy bear and baby blanky often while sucking his thumb, on the other hand he's pretty perverted and constantly hits on women.
* Luanne Platter from the later episodes of ''WesternAnimation/KingOfTheHill'' when she began dating and eventually married a moronic, middle aged, hillbilly "Lucky" to the point where she acts like a five year old most of the time.
** Peggy Hill was once described as a woman-child, possibly due to her self-centeredness.
** [[AdultsAreUseless Most of the adults are immature in some way]], to the point where ''[[TheDitz Bobby]]'' snaps after his grandpa and step-grandma leave him to care for grandpa's infant son and Luanne and Lucky prove to be ridiculously irresponsible parents (I think Luanne is pregnant at this point).
** Hank's boss, Buck Strickland, is so childlike to the point where Hank always have to bail him out whatever trouble he gets into.
* ''WesternAnimation/KingRollo'''s daily schedule is indistinguishable from that of a five-year-old boy. His kingdom doesn't seem to suffer too much from his behaviour, though.
* ''WesternAnimation/TheLegendOfKorra'': Despite having grown up an orphan living on the streets, Bolin is pretty immature for his age and circumstance. Justified in that his older brother Mako has done a lot to shelter him from the worst aspects of their lives, and essentially raised him on his own. There's a tinge of deconstruction to Bolin's treatment because it shows the consequences of raising a manchild on the person who shelters them from reality. Mako is emotionally stunted due to having fixated for so long on raising Bolin. His romantic relationships feature him playing the part of [[DeclarationOfProtection a protective figure]], and when a girl proves she doesn't need his help he loses interest.
** Also Aang and Katara's son Bumi although he's a middle aged man he acts like a hyperactive, childish prankster, his sister Kya lampshades this at one point:
-->'''Kya''': Even though you're the oldest you've always acted like the youngest
* WordOfGod on ''WesternAnimation/{{Madagascar}}'' and ''WesternAnimation/ThePenguinsOfMadagascar'' is that RidiculouslyCuteCritter Mort the mouse lemur, who looks and acts like a child, is [[OlderThanTheyLook the lemur equivalent of a thirty-five-year-old]]. Julien has tendencies this way as well; he's constantly demanding attention and throws tantrums when he doesn't get what he wants, but at the same time gets very upset and starts talking to his plush toys when he's lonely, and [[spoiler:it's revealed via the magic of the Golden Squirrel that his greatest desire is simply to have his friends near him]].
* Peppermint Larry from ''TheMarvelousMisadventuresOfFlapjack'' became this in the second and third season. Heavily lampshaded [[spoiler: during his BiggerBad, EvilAllAlong, TheDitz and TookALevelInDumbass roles]].
* Toki Wartooth from ''WesternAnimation/{{Metalocalypse}}''. He has a teddy bear, eats candy, collects model airplanes, says "Wowee", and has a childish naivety for certain subjects such as sex. He also drinks, swears, and [[spoiler:goes on the occasional murderous rampage]].
* Texas ''and'' Tooley in ''WesternAnimation/{{Motorcity}}''. When the former is telling the latter about "his" exploits, Tooley even lies down like a kid would.
* ''WesternAnimation/MrBogus''.
* The main characters of ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' are all responsible young adults, more or less, setting aside when they need to be relatable to young children. However, Pinkie Pie acts like an excitable six year old and seems incapable of holding a serious conversation or actually reading the mood. She can be surprisingly neurotic whenever events aren't as exciting as possible or if she isn't getting the kind of attention she wants.
** Princess Luna tries to assert an air of cool authority, but it doesn't take much for the mask to break and this trope to come out. Endlessly enthusiastic about everything, she has a HairTriggerTemper and will sulk endlessly if she doesn't get her way. She is desperate for authority, but tends to resent it when it is actually given to her. Appropriately she gets along very well with children.
* Oggy from ''OggyAndTheCockroaches''.
* Kyösti Pöysti in ''{{Pasila}}''.
* Dr. Doofenshmirtz from ''WesternAnimation/PhineasAndFerb'' is physically in his 40s, but mentally around 10.
* The Mayor from ''WesternAnimation/ThePowerpuffGirls'' eventually wound up becoming this.
* Ray Stantz, one of ''WesternAnimation/TheRealGhostbusters'', is a more subdued version of this trope. While mature and perfectly capable of looking after himself, Ray still possesses an almost childlike idealism and enthusiasm for life. Ironically, this actually helps the Ghostbusters lure the Boogieman when they learn that the monster is attracted to people who think like children.
* Pops from ''WesternAnimation/RegularShow'', save the fact that he's the opposite of LiteralMinded.
** Rigby is this too. He may be 23, but he acts like an out of control teenager most of the time.
** Mordecai, to a lesser extent. He's a lot more level-headed and less impulsive than Rigby, but just as eager to slack off and do childish things.
* Homer Simpson from ''WesternAnimation/TheSimpsons'',. The most immature in the family, even more so than his son Bart. Especially after Season 10.
* Randy Marsh, Stan's father from ''WesternAnimation/SouthPark'', has become this in recent years.
* ''WesternAnimation/SpongebobSquarepants''. He's old enough to hold down a job and live on his own, but is so immature and goofy that he's been referred to as a kid on multiple occasions.
** & Patrick Star [[UpToEleven even more so.]]
* The Warden of ''WesternAnimation/{{Superjail}}''. Even lampshaded by the Mistress.
* Amethyst from ''WesternAnimation/StevenUniverse''. Some of her antics are reminiscent of a teenager acting out. Her yelling "I don't wanna!" when Garnet tells her to go back to the temple in "Tiger Millionaire" is a good demonstration. [[spoiler:She's actually quite young in comparison to the other Gems, having been created on Earth instead of hailing from Gemworld.]] This is further enforced by the fact that during Greg's flashback in "Story for Steven" she's much younger in appearance than she is now.
* ''WesternAnimation/{{Thundercats}}'': At the beginning of the series, Lyon-O was placed as a child in a stasis pod to keep him from aging while Jaga drove their spaceship to the third planet. His pod was damaged and functioned imperfectly, so unlike the others he still physically matured inside and he eventually left it as an adult, thus making it a case of JustifiedTrope.
* ''WesternAnimation/XiaolinShowdown'': Kimiko's Dad is a child on the inside. Or so she once told her friends.
* As with the comic example above, Captain Marvel in ''WesternAnimation/YoungJustice'' is really a kid. However, none of the teens know his real form, so he definitely comes off as being this trope.
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