- Corpse Party has Yoshikazu Yanagihori, formerly a Cool Teacher. As his mental illness progressed, he reverted to a childlike mental state, and eventually couldn't even convey his thoughts. People noted that he was still the same person he was before, so it was shocking when news came out that he abducted four children and brutally killed three of them. He didn't actually kill the children. He was manipulated into kidnapping them, but he was just an accomplice to the real killer... the surviving child, who was actually a malevolent spirit.
- King Erik from Fantasy Life not only acts like a child but looks like one despite having a middle-aged wife and an at least teen-aged daughter. It turns out he's in a magic-based prank war with the equally man-childish Former Dark Sultan of Al Majiik and that one of the spells turned him into a child.
- Snow Villiers in the Final Fantasy XIII trilogy, mainly the first two games. His go-getter demeanor combined with his hero complex tends to rub some people the wrong way. Lightning considers Snow an irresponsible idiot incapable of caring for Serah let alone taking care of himself. She can't stand Snow for his recklessness and disregard for proper manners and authority, calling him "chummy" and "arrogant", comparing him to a gang leader putting others in danger so he can play the hero. In Final Fantasy XIII-2, Noel is equally irritated by Snow's brashness and tendency to charge into danger without thinking or considering the potential consequences.
- Yellow Heart, from Hyperdimension Neptunia Victory. Despite being physically powerful and having the visible age of the other CPUs (at least), she does everything to please her "parents", can only read and write very simple words, and is generally sharp as a sack of particularly dull hammers. Turns out she's an artificially altered Peashy, and therefore actually a child, despite "the big me" looking like an adult.
- Tingle from The Legend of Zelda series. A 35-year-old man who believes he is the reincarnation of a fairy and spends his spare time floating around on a balloon searching for other fairies. Ramped up in The Legend of Zelda: The Wind Waker, where his HQ is a tower where his cohorts spin the top around to make magic happen... or something.
- Link in The Legend of Zelda: Ocarina of Time is a version of this - albeit a sympathetic version that totally makes sense since he was a child that was in slumber for seven years and finds himself in a young adult body. Some of the text in the game reminds you that even though he looks grown and is battling some nightmarish monsters, Link is still a child.
- Mae from Night in the Woods is a twenty-year-old college drop-out who acts like a rebellious teenager, compulsively committing petty crimes and having a hard time talking to other people her age about more adult concerns. This strains her relationships with her parents and most of her friends, except her partner in crimes, Gregg.
- Adding the "Childish" trait to a Sim in The Sims 3 will result in one of these. In addition to their Fun meter depleting more quickly, they'll be more prone to watching the children's television channel, can play tag and play with children's toys (options normally unavailable to older Sims), among other things. Adding the "Evil" trait alongside this one can result in the psychopathic version of this trope, too.
- Super Mario Bros.:
- Mario easily fits into this category, though he's a distinctly positive portrayal of it. Aside from being a never-ending fountain of bubbly joy, he has absolutely zero qualms with playing with the Mini Marios his own company manufactures, indulges himself in any kind of fun activity regardless of how juvenile, and seems perpetually impossible to take the life-threatening obstacles he overcomes with anything but a whoop of excitement and charging headlong at it.
- Mario might be full of youthful exuberance, but Luigi often just comes across as childish and immature. It is particularly evident in the Mario & Luigi series, where he's prone to crying like a child, though later games in the series tone it down some somewhat. Superstar Saga and Partners in Time has loud, exaggerated sobbing, Paper Jam has him quietly crying into his hands. Even his voice comes across as more childish than Mario's, despite Mario having the more higher pitched voice of the two.
- Bowser shows obvious signs of immaturity on a regular basis; he has nasty mood swings that scare even his most loyal servants, he never feels responsible for his failures, always looking for someone else to blame, and he is never satisfied with what he already has (he has castles in almost every land in the world), always wanting more. It gets even funnier when he meets his baby self in Partners in Time: barely anything differentiates them in terms of personality, which clearly shows that Bowser has barely evolved mentally since his infanthood. No wonder why Kamek lacks patience...
- Most Hack and Slash Protagonists created and directed by Japanese developers like Hideki Kamiya and Hideki Itsuo, considering the trope consists of over the top flamboyant badasses that literally act like teenagers when dealing with hordes of demons/angels. They most certainly qualify.
- Most of Capcoms most famous protagonists(with a few exceptions) are all manchildren/womanchildren with special abilities, quirks, and near emphasized cartoon quirks that highlight their games. Like Morrigan as an overstimulated sex demon with a teenage party girl mentality, or Date Masamune a brash and rambunctious feudal lord turned Japanese delinquent.
- Justified in the case of Grunt from Mass Effect. Since he didn't technically HAVE a childhood (unless you count accelerated growth in a vat while a Mad Scientist plays context-free videos for you to be a "childhood"), he comes out of the tank nearly fully grown but without a great deal of comprehension of the world beyond "if you squeeze this thing here, the gun goes bang and kills something". As a result, while he's fairly smart, he still plays with action figures, pulls out Buffy Speak on a regular basis, and mostly views Shepard, the player character, as a Parental Substitute who will teach him how to do all the important krogan things like break stuff and set it on fire. In the Citadel DLC, after he sets a Citadel Security car on fire, steals it and crashes it, this exchange can happen:Shepard: Grunt, apologize to the nice man for setting his car on fire.
Grunt: (looking at his feet) I'm sorry I set your car on fire...
[notices Shepard's expression]
Grunt: ...and I won't do it again.
[...and as soon as the police have left]
Shepard: I love you, Grunt.
- Metal Gear:
- Big Boss, of all people, in Metal Gear Solid 3 and Metal Gear Solid: Peace Walker. He has a Phobia of vampires, he gets ridiculously excited about eating things, he makes childish noises of disappointment when told not to eat things, is rather fixated on his mother figure, thinks making cardboard tanks and using bananas as firearms is a pretty neat idea, gets along as equals with a literal child, and still believes in Father Christmas.
- Otacon in his first appearance in Metal Gear Solid comes across this way. He's an intelligent but naive tender-hearted dork who likes dogs, robots, and anime and just wants to build cool stuff to protect people, and he is way out of his depth in a cast full of conspirators and killers.
- Raiden in Metal Gear Rising: Revengeance is this at best, and a Psychopathic Manchild at worst. His previous appearances had shown him as somewhat adolescent in personality but definitely a grownup; but in Revengeance, he begins reverting to the child soldier he had been in the 1980s, interacting as equals with children despite being a father, and showing a rather bratty side, even aside from all of the ruthless murdering.
- One interpretation of N's character in Pokémon Black and White. It's not played for laughs. Indeed, it may actually be Foreshadowing of his... father issues.
- Heck, N's upbringing in general does a lot to explain his Manchild tendencies, especially when you see his toy room.
- Sonic the Hedgehog games:
- Doctor Ivo "Eggman" Robotnik has shown some shades of this. In spite of his advanced knowledge of science and robotics, Eggman also appears to be very immature and is prone to throwing childish outbursts whenever something doesn't go his way. His television and comic depictions also exhibit some of these traits, most notably his Adventures of Sonic the Hedgehog counterpart.
- Vector the Crocodile is also an example. Despite being 20 years old, he's no more mature than the rest of Sonic's gang, often arguing with 6-year-old Charmy Bee.
- F.A.N.G. from Street Fighter. He prances around and gleefully follows Bison's orders like a child and whenever his plan goes wrong he is prone to throwing temper tantrums. It's safe to say his other fellow Shadaloo lackeys have little patience for his shenanigans.
- Luke fon Fabre from Tales of the Abyss starts out very gullible, emotional, demanding, self-centered, petulant, frustrating and stubborn. Most of the time, he acts like he's seven years old. Which makes sense, because technically, he is. He was cloned from the real Luke fon Fabre seven years prior to the game's opening, and retained none of the original Luke's memories.
- In Undertale, Papyrus, who is built like an adult man despite technically not being human and having an unclear age, has a few distinctly childish tendencies. In particular, he has his brother read bedtime stories to him, and is particularly fond of one titled Peek-a-Boo with Fluffy Bunny ("THE ENDING GETS ME EVERYTIME").
- Max Hass from Wolfenstein: The New Order is an almost literal version, due (presumably) to the fact that a good 1/4 of his skull is missing. His room is filled with toys (some of which you can go out of your way to recover for him at the base), and he's got an acute fear of loud noises (namely buzz saws).
- Yakuza: Subverted with regards to Pocket Fighter in 0 and Kiwami. While he is obsessed with the rather childish hobby of slot car racing, he is an otherwise mature and well-adjusted individual, and even expresses concern that his hobby might be hampering other aspects of his life.
Man Child / Video Games