A common trope among Child Prodigies and Brainy Babies: an intelligent youngster is essentially an adult in a child's body. They have no interest in ever being a child. They eschew toys in favor of books and beginner scientific equipment. They immediately and eloquently denounce the logic of Santa Claus. They may insist that their parents read the classics to them as bedtime stories and thus scoff at the books meant for their age. Or they just read the classics to themselves purely for fun. They would rather discuss world events than...play (How childish!). They may even already have a distinct, philosophical worldview, never mind that they haven't lived long enough to see enough of the world to form such a view. And so on. Another common effect of this 'adult-in-a-child's-body" phenomenon is that characters who act their intellectual age have no interest in kids who are their actual age. They may look down on kids their own age as savage or barbaric, and would rather associate with their intellectual peers, even if those peers are 4 or 5 times the character's age. Strangely, in the world of TV and media in general, neither party seems to care about the age difference, and the kid genius in question thinks nothing of it to discuss the latest political development with someone old enough to be their father/mother. Thus, of course, they are likely to be construed as teachers' pets in any academic setting. This aspect is only occasionally Truth in Television, as there are many cases of highly intelligent students deliberately dumbing themselves down in order to fit in. Often, a character who acts their intellectual age is, supposedly, more sophisticated than the adults, even the educated ones, and will not hesitate to point out grammatical errors, logic flaws, or to criticize behavior. Often may grow into an Insufferable Genius, if they are not one already. If they're lucky, they may instead outgrow their uptight arrogance and wind up a Recovering Insufferable Genius. Note that this refers to kids who more or less behave like adults while still functioning in the world of kids, and having a normal childhood (or as close as a child prodigy can get to normal). If they are highly intelligent but thrust into an adult role, or otherwise traumatized into maturity, then they are Wise Beyond Their Years
- River Tam from Firefly. She's shown, in flashbacks, to have been so smart that she could spot flaws in the textbooks Simon was studying from and uses surprisingly advanced terminology ("that whole section is fallacious"). Of course, she's also shown as being quite willing to be silly and engage in age-appropriate activities (like pretending she's an Alliance soldier who has gotten cut off from her squad when the Independents brought in dinosaurs).
- The Whatelyverse has several examples. Ayla springs to mind as a self-acknowledged one, and Jobe is one who doesn't realize it. Ayla's reaction to realizing this is to try and bring his friends up to his level, so that they can at least understand why some things bug her so much. ("Why would I blow money on an expensive stereo system that's going to be outdated in three months' time, or on clothes that are going to be out of style in two weeks?")
- Manny from Modern Family. In one particular episode, he has been having conversations with a grown woman online and arranges a date, neither suspecting an age difference.
- "He's an old soul."
- Devon in Lawn Dogs is a rare aversion. She is an extremely intelligent child, much smarter than any of the adults around her, but she still actually acts like a child.
- Micah in Heroes is an example of this.
- The "Dakota Fanning" series of skits on Saturday Night Live is made of this trope. An actress portraying a fictionalized version of Fanning behaves this way
- Charles Wallace from A Wrinkle in Time, which leads to him overestimating his capabilities, and gets him ensnared by IT.
- Artemis Fowl...most of the time. Subverted in the beginning of The Lost Colony, when among his greatest nemeses is the distraction that is puberty.
- One of the first novels to feature a Child Prodigy was The Hampdenshire Wonder in 1911. The protagonist is not only a genius, but a truly superintelligent little kid who judges the whole human culture an "elementary, inchoate, disjunctive patchwork"... at age four and a half.
- Wensleydale in Good Omens: His parents "called him 'Youngster'. They did this in the subconscious hope that he might take the hint; Wensleydale gave the impression of having been born with a mental age of forty seven." His favourite "comic" is Wonders of Science and Nature, and he insists on being the Only Sane Man in the face of Adam's ideas.
- Aaron Fidget in Hogfather:
Aaron: Let's be absolutely clear. I know you're just someone dressed up. The Hogfather is a biological and temporal impossibility. I hope we understand one another.Death-as-Hogfather: Ah. So I don't exist?Aaron: Correct. This is just a bit of seasonal frippery and, I may say, rampantly commercial. My mother's already bought my presents. I instructed her as to the right ones, of course. She often gets things wrong.
- Thomasina in Arcadia by Tom Stoppard. She functions as a child with regards to romance and sex, and an adult with regards to intellectual matters (Classics scholar, mathematical genius). Which serves as a reflection of the Central Theme of the conflict between Romanticism and the Enlightenment.
- Van from Harvest Moon: Animal Parade prefers studying to playing, and always wants to know if your kid likes to read/go to school/do homework. He even teaches some of the other kids during events!
- Egghead, Jr. in the Foghorn Leghorn cartoons. He was always reading books and otherwise acting in an intelligent manner, and didn't want to do the childish things Foghorn Leghorn wanted him to do.
- Subverted with Polly from Stickin' Around. She plays off this trope accordingly, though it doesn't stop her from playing with the other kids.
- Stewie in Family Guy tends to zig-zag this trope.
- Dexter in Dexter's Laboratory adheres to the trope, except that his attitude toward girls remains entrenched in normal six-year-old mode.
- Lampshaded in a recent American Dad! episode with a flashback of Steve's friends as toddlers:
Young Barry: Interesting how we've developed such a sophisticated hierarchy at this young age.Young Steve: Shut up, Barry.Young Barry (enthusiastic): I'm at the Bottom!
Hello, Unknown Troper. You'll need to get known to lend a hand here.
Three days must pass before this YKTTW is Launchworthy or Discardable