Bart Simpson: Mom, when you give that lecture, you're boring Springfield.
This is what you get when a child believes they know better than adults, except this time, they can prove it.
Almost always on the side of good, most likely belonging to the Chaotic Good category, this character isn't an indiscriminate back-answerer like the Bratty Half-Pint but rather steps up when an unreasonable or outright abusive authority figure tries to do something stupid or horrible (or just simply when adults do something he or she finds stupid), instead of submitting quietly to their authority. What separates them from your average Kid Hero is their snarkiness about it, at least at first.
In the '50s the Mouthy Kid would have been slapped upside the head and shipped off to the Military School. Children were little angels, or at least tried to be (Leave It to Beaver, My Three Sons, Family Affair). That all changed with Arnold on Diff'rent Strokes. Television parents have been dealing with attitude ever since.
Likely started out as a subversion of the Children Are Innocent attitude that had prevailed since Victorian times.
- Crayon Shin-chan: Shinnosuke "Shin-chan" Nohara, although he is a five year old whose dialogue is pretty much "farty poop fartfart", he crosses the realism line once he calls his mom flat-chested (in both the original and the Gag Dub).
- Fullmetal Alchemist: Edward Elric gets called out for it at one point. "An Edward who can't use alchemy is just another kid with a foul mouth."
- Mazinger Z: Shiro Kabuto. He is a Deadpan Snarker who has no trouble telling exactly what he thinks. His older brother, Kouji Kabuto finds them annoying sometimes because Shiro often thinks his actions or plans are dumb. He also appeared in Great Mazinger.
- Getter Robo: Genki Saotome is another example of a child who often tells what he thinks; a trait that is not appreciated by the adults and teenagers he meets.
- Thanks to being Older Than He Looks even before Immortality, as well as an all-around smartass, Firo Prochainezo gives off this impression to nearly everyone he meets even between the ages of nineteen and ninety.
- The odd case of Czeslaw Meyer, who has been ten years old for a couple hundred years. While he had a pretty rough time of things, someone decided to Throw the Dog a Bone and give him a normal life. He spends the next seventy years in the novels invoking this trope, particularly while Walking the Earth.
- Super Milk Chan: The title character is this. In the [adult swim] dub she regularly calls her friends dumbasses.
- Yuuki from Baby Steps, the youngest member of Love Interest Natsu's tennis club who originally thought the protagonist Eiichirou was either a spy for another club or a "degenerate old stalker". Since then, he never misses an opportunity to give E-chan a hard time.
- Ayane's High Kick has Ayane's annoying younger brother Kenta, who we first see butting into an argument between Ayane and her mother about Ayane skipping school to attend a pro-wrestling tryout.
"There's no choice. Big sis isn't very bright, so she has to make a living with her body!"
- Bikky in FAKE is a particularly mouthy Bratty Half-Pint. Especially when he's mouthing off at Chivalrous Pervert Dee whom he sees as nothing more than a Handsome Lech chasing after his adoptive father Ryo.
- Shippo from InuYasha is this in his wiser moments.
- Mouth in The Goonies is appropriately nicknamed. "Shut up, Mouth!"
- Ronnie, a middle schooler of hilarious retorts and apparently vast cinematographic knowledge, in Role Models
Danny: Pick us up in two hours.
Ronnie: Fuck you, Miss Daisy.
- Watch the Birdie, an early Bob Hope Short Film, has a mouthy little girl.
- Star Wars: The young Anakin Skywalker from The Phantom Menace was given this characterization. He may be a kid with an attitude, but he's still well-meaning and have a reputation to build and repair anything. He's also willing to risk his own well-being to help others in need.
- In fact, a deleted scene implies he gets into fights. The scene shows Anakin fighting another young Rodiannote who accused him of cheating in the Pod Race.
- Mouthing off is the least of the various mischevious behavior Addie Loggins from Paper Moon gets into — she also smokes, runs con rackets, and sets up an embarrassing bedroom encounter with Gold Digger Miss Trixie.
- In Time Enough for Love, protagonist Lazarus Long travels back in time to meet his family in 1917 Kansas City, Missouri. There he encounters his past self, Woody, who is already an up-and-comer, about as shrewd, stubborn, and mouthy as it's possible for a five-year old to be, and kept in line only with generous application of paddle to arse. His (and Lazarus') grandfather Ira remarks — in unknowing irony — that the kid is going somewhere, if he somehow makes it to adulthood without being murdered by his parents. He has no idea.
- Matteo Ta'anari in Someone Else's War. But only to kids his own age—never to adults or small children. And he doesn't get shipped off to military school so much as shipped off to the military.
- Cory Matthews in Boy Meets World was this in the first season. Subverted in that he often doesn't know better than the adults which is the entire point of each episodes with him admitting he doesn't know better by the end of each episode
- Dennis the Menace: Seymour Williams, to John Wilson in the final season.
- Modern Family: Alex, the middle child. She does little else on the show than make snarky comments.
- Leave It to Beaver: Exception that defines the rule: Eddie Haskell — bratty around his peers, but with a nice phony front of shallow flattery while he was around adults.
- Malcolm in the Middle: All of the boys. Francis is sent off. His advice helps keep Malcolm from the same fate.
- The Partridge Family: Danny Bonaduce's character is bratty around his peers but puts on a nice front around adults.
- Darlene Connor of Roseanne epitomizes this trope in the early seasons until she grows into quite the Deadpan Snarker as the show focuses more on her. DJ also sometimes fell into this trope as well.
- Skins: James Fitch (Katie and Emily's kid brother), most likely due to the influence of his (unseen) friend Gordon MacPherson.
"I want fish and chips! This tastes like bollocky wankshite!""Gordon MacPherson says you call them dykes, because you have to stick your finger in them.""I want to fuck Naomi [beat] I do, get over it."
- Welcome Back, Kotter: While the Sweathogs are considerably older than the usual Mouthy Kid, they form an obvious precedent.
- Bad Boy: Moon Won In in this Korean Drama, as she sneaks beers from her sister, tries to buy cigarettes even though she's underage, and in one episode steals money from an apparently unconscious man.
- Possibly the Ur-Example, Fanny Brice's Baby Snooks was somewhere in between this and Constantly Curious. Her sole reason for existence appeared to be to drive her father to the very brink of insanity, but she did it without apparent malice — just pure innocent mischief. And given that the character was created in 1912, and continued to be wildly popular until Brice's death in 1951, it shows that Arnold from Diff'rent Strokes far from created the trope — he just incarnated it for a new, more relaxed generation.
- In Fallout 3 there's a town called Little Lamplight, which banishes its residents when they turn 16. Because of this, the town is filled with kids who walk around swearing because there's no one to tell them no. In fact, the mayor's greeting to you is basically "who the fuck are you?".
- Nall's human form in Lunar: Eternal Blue, at least that's what he seems like at first...
- Loki from Bayonetta 2 has an extremely snarky demeanor and swears quite a lot whenever he's on screen, getting him into a few sarcasm duels with Bayonetta. He's so mouthy, for that matter, that he isn't afraid to snark off to the Masked Lumen.
Loki (to the Sage): You again? Listen mate. One, the mask is shit. OK? And two, get out of my way.
- Criminal Case have Elliot Clayton, a 17-year-old smart alecky member of the Bureau who constantly finds new ways to mock the other team members' intelligence.
- In the Jacksepticeye fan game The BOSS, Billy definitely qualifies, as he constantly snarks at Jack.
- Amber from The Free Willies always responds to virtually anything the antagonistic teacher Mrs. Setzer says with an insult. Or a string of insults.
- Pretty much every child on Something*Positive is as snarky as the adults, and usually shut down whatever strawman they're facing with a well-aimed barb.
- Sylvester, from Twig, enjoys his backtalk as much as the next twelve-year-old science experiment, but his friend Lillian, The Team Normal who is responsible for keeping Sylvester and his fellow experiments working in the field, also loves to interrupt older and more experienced doctors to show them up with her greater field experience.
- Beavis and Butt-Head: Mike Judge said that dialogue is a better reflection of the real-life Mouthy Kid — not too clever, relies heavily on toilet humor — because in reality, kids aren't as smart as a roomful of Harvard-graduate writers.
- Toph Beifong from Avatar: The Last Airbender practically defines this trope. She is not afraid to speak her mind or tell someone off, no matter their position or title in life.
- Helga in Hey Arnold!. She's a Stepford Snarker who uses insults, sarcasm and threats to cover up her insecurities. Since everyone around her treats her like crap, she's got plenty of reason to be mouthy.
- Star Wars: The Clone Wars: has Ahsoka Tano in a very odd example, seeing as Jedi Padawans are encouraged to be respecteful.
- Russell from Fat Albert and the Cosby Kids, being Bill's little brother, was the youngest one in the group. He also had the biggest mouth as a majority of his dialogue was something sarcastic or insulting. Rudy was usually his favorite target, granted Rudy was usually asking for it.