So, there's this quality I've noticed in some fictional kids in TV, movies, books, wherever. It's hard to pinpoint exactly what the quality is, as there's overlap with a number of different tropes, such as wise beyond their years, adorably precocious child, child prodigy, acting your intellectual age, etc. Even little miss snarker could qualify. But while the kids who fall into the category I'm thinking of can display any one or more of these qualities, and undoubtedly some of the kids mentioned on the pages I've linked to are characters I'd include on my own list, the quality I'm thinking of doesn't necessarily fit neatly into any of those tropes. And I'll include some kids on my list that aren't on any of TV Tropes' pages. One thing I do want to point out is that I'm generally only going to include pre-teens, though there might be rare exceptions who are like 13 or 14 (particularly if I'm unsure of a character's age). The teenagers from Dawson's Creek or Daria, for example, are definitely too old to qualify. I should also say that my list will be entirely subjective; you might find yourself agreeing with some of my choices and disagreeing with others. (Or never having heard of some of my choices. Or having choices of your own that I've never heard of or wouldn't agree with.) What I'm going for, here, is kids who possess a certain emotional maturity, an understanding of the world that is beyond that of most kids their age, and an ability to interact with adults on a mostly adult level (and often be taken seriously as such, by adults). Which is not to say they're entirely grown-up in their thinking; they're all still actually children, after all. And... I don't know what else to say, so let's just get on with the list.
See also TV's Most Precocious Kids (TV Guide)
(500) Days of Summer
Rachel Hansen... was probably about 12 in this movie. I don't remember anything specific about her, but I did call her precocious in my review, so...
Adventures in Babysitting
Sara Anderson is certainly snarky beyond her years, and seems to have a somewhat better understanding of the world than your typical 8-year-old.
Anna-Kat Otto (7 at the start of the series) has OCD, which makes her seem strange to a lot of kids her age, though she does have some interests typical of girls her age. However, she's also very clever (certainly moreso than her teenage sister), and has a very mature understanding of the world.
Anne of Green Gables
12-year-old Anne Shirley... what can I say about her? She's smart, she's got a great imagination, a great love of literature, a generally mature outlook on life, very spirited and outspoken... She's pretty much the prototype for the precocious child trope.
Avatar: The Last Airbender
While I'm not sure I thought much about the characters fitting into the "precocious kid" trope until I started this page, they kinda do. I mean, 12-year-old Aang is very much a kid in a lot of ways, but he also has the maturity of someone basically raised by the equivalent of Buddhist monks. On top of that he has to deal with things I won't get into, to avoid spoilers, but they're the kind of things that would make anyone grow up in a hurry. The same can also be said for many of the other characters, for their own reasons, though since they're in their teens, I won't mention them specifically. (Even though they may have become mature beyond their years prior to the start of the series, when they were young enough to qualify for this list.)
Ben and Kate
I don't remember this show well enough to give specific examples, but 5-year-old Maddie Fox was definitely precocious.
I don't remember this show well enough to give specific examples, but 8-year-old Charlie Meyers was definitely precocious.
Better Off Ted
Rose Crisp (7 at the start of the series) is often very insightful, and acts as her father Ted's confidante and often his moral compass. She's actually one of the characters that first made me start thinking about this trope, when the show aired in 2009, though I didn't get around to actually starting this page until 2020, a decade after the show ended.
10-year-old Huey Freeman is one of the most intelligent, mature, wise beyond their years, socially conscious characters on this list, and awesome in pretty much every way. Easily the most mature character on the show, especially compared to some of the adults.
The Cleveland Show
5-year-old Rallo Tubbs basically acts like the star of a 1970s blaxploitation film, except that he's stuck in a life that is nothing like one of those films. And, oh yeah, he's five.
The Cosby Show
Olivia Kendall (3 when she joined the series in season 6) is a fairly precocious child, and I think it wouldn't even occur to her not to speak to her elders as if she's on their level (though not to the extent of being disrespectful).
Maya Hayes (10 years old). I called her precocious in my review, so I guess I should include her here, even though I don't remember the movie very well.
Stewie Griffin is a toddler and an erudite super genius, though pretty much the only person who recognizes that he's anything more than a normal toddler is Brian (a talking dog who is inexplicably best friends with Stewie's father).
Field of Dreams
The young Karin Kinsella (I don't know her age, exactly, but definitely in the single digits) has few lines in the movie, but they're good ones.
Basically all the middle school kids talk and act like adults because the whole show is a parody of a 1970s cop show, or whatever.
Fresh off the Boat
Evan Huang (about 8 at the start of the series) is very smart, very driven to succeed, and already has his future mapped out. His best friend is his mother, Jessica, and he takes an active role in the neighborhood association (which basically consists of adult women).
Gabby Duran & the Unsittables
Olivia Duran (I guess she's about 10 at the start of the series) is very smart and mature for her age.
I'm not sure how old Michelle Bauer was when I watched this show in the early 90s; she might have been a pre-teen when I started watching, or barely into her teens. Anyway, I just remember always thinking she seemed wise beyond her years. (At least until Rachel Miner was replaced by another actress and the character became mostly a more typical teenager.)
His Dark Materials
12-year-old Lyra Belacqua (or as she's later known, Lyra Silvertongue) certainly has a great deal of cunning for her age, and an adventurous and heroic spirit. She also has a preternatural ability to read an alethiometer without having studied books about it.
8-year-old Brendon Small and his friend Melissa Robbins are fairly normal kids, but they're both quite comfortable conversing with adults on their own level. Their friend Jason... I dunno, maybe not so much. He mostly seems to have a less mature mind than the other two.
I Could Never Be Your Woman
I don't remember this movie well, but I do remember thinking 13-year-old Izzie Mensforth was somewhat precocious, even if I couldn't say in what way.
7-year-old Gertie Trinké is precocioius in various ways, not least of which is a passion for the play "Sweeney Todd."
The Legend of Korra
Jinora (10 at the start of the series) is the eldest child of an airbending master, in this spinoff of "Avatar: The Last Airbender." Like Aang, Jinora has the sort of wisdom and maturity of someone raised by the equivalent of a monk (though this is far less obvious in her younger siblings).
Tracy Callahan. I don't remember the show very well, but I find that I called her precocious in my review, so I should mention her here.
Life on a Stick
Gus Lackerson (9 years old) sounds precocious based on my old review of the show, but now I don't remember him at all.
Trixie Espinoza (7 at the start of the series) seems to display a roughly equal mix of childlike innocence appropriate to her age and a somewhat more mature understanding of some things. And she doesn't hesitate to think of certain adults as friends.
Brick Heck (8 at the start of the series) probably qualifies, though I haven't really seen enough of the show to be quite sure.
Manny Delgado (10 at the start of the series) has always talked an acted like an adult (and a pretentious one, at that). I'd say he seemed wiser and more mature at the start of the series than he did by the end of the series. Lily Tucker-Pritchett (a baby at the start of the series) has talked in a precocious (mostly snarky) way since she was about 3.
My Wife and Kids
Franklin Mumford was, I think, about 7 or 8 when he was introduced in the third season. He's a genius, and often has conversations as an equal with his girlfriend's father, Michael Kyle.
Grace Sheffield was about 7 or 8 at the start of the series. She was in therapy, and often spoke with an understanding beyond her years.
9-year-old Dick Butkus is highly intelligent and wants to be taken more seriously by his father, Larry Bird. There are also shades of precociousness in the way 9-year-old Max Weaver and his 6-year-old sister Abby talk to adults (rather snarkily).
Pretty much all the kids on the show act like adults, because of the nature of their jobs.
11-year-old Jim Hawking is definitely smarter and wiser than his adult business partner, Gene Starwind.
I'm not sure how old Linus van Pelt is supposed to be (surely under 10), but while in some ways he acts younger than his age (he famously carries a security blanket everywhere), he's definitely the most philosophical kid from the Peanuts comics and specials.
Phineas and Ferb
Aren't Phineas Flynn and Ferb Fletcher a bit young to create so many astonishing creations? Yes, yes they are.
Phoebe in Wonderland
I don't remember much about the movie, but I called 9-year-old Phoebe Lichten and her younger sister Olivia precocious in my review, so I'll assume they belong on this list.
10-year-old Mikey Blumberg... well, let's just say he's an old soul.
I vaguely recall thinking that 12-year-old Puddle Kadubic fit this trope, when I watched the show, but I don't remember it well enough to give any specific reasons.
8-year-old Lisa Simpson is the smartest and most mature member of her family; possibly her whole town.
This is the show that really cemented my desire to start this page. I think all of the kids on the show are precocious to some degree, but I think the most precocious is Sophie Cooper (around 8 at the start of the series). She's smart, and always seems to have a mature understanding of things. (One time a friend of Sophie's dad even told her, "Sorry, I keep forgetting you're not an adult.") Then there are twins Amy and Emma Fogerty (around 7 at the start of the series). I think of them as adorable sociopaths. They're clever and good at a lot of things, always taking on adult responsibilities (to some extent they raise themselves) and talk to everyone somewhat condescendingly. There's also Rory Banks (around 10 at the start of the series), who always has lavish ideas for projects, and likes to take a leadership role among his younger friends, as well as being outspoken with adults. Graham D'Amato (around 8 at the start of the series) is the kid who acts his age (or perhaps even younger) the most, but he also has his moments of maturity.
Someone Like Me
I don't remember this show well at all, but I have a feeling 11-year-old Gaby Stepjak fit this trope.
Molly Johnson was I guess like 12 years old in the movie (according to Wikipedia). She's very bright, especially when it comes to politics, and she often acts almost like a mother to her father, instead of like a daughter.
Allie Keys was, I think, 8 or 9 years old for most of her on-screen time (she narrated the entire miniseries, but didn't appear until the last half or so). She's actually well beyond "precocious," and there's a very good reason for that...
Just watch the scene where Buck interrogates his 8-year-old nephew Miles Russell, and you'll see some precociousness, I promise.
Ray Schleine is only 8, but she's been forced to grow up quickly because of absent parents.