In Real Life, it is generally accepted as a fact that people grow smarter and wiser as they get older. Therefore, whenever a younger character turns out to be right over an older character, it's considered shocking or hilariously ironic. This trope can come into play if the child in question is Wise Beyond Their Years, but is brushed off or ignored because they're still Just a Kid. It needn't be limited to children vs. adults either; it's just as apt to arise in debates between adults of different generations, complete with references to the age gap.
This may be a case of Truth in Television to some degree. A younger generation often brings a fresher perspective to a situation than their elders, and they may also be more willing to question traditional concepts. What is more, novelty has no particular stigma for them, since for them most things are new.
Compare Adults Are Useless.
Not Now, Kiddo is the inversion of the trope.
- Dragon Ball Z provides a considerably dark example during the Cell Saga, when Gohan, in a state of Revenge Before Reason, deliberately drags his Curb-Stomp Battle with Cell out solely because he wanted him to suffer as much as possible for his crimes. While Goku and the other Z-Fighters are rightfully horrified and urge him to finish Cell off right away, Gohan is far from wrong that Cell deserved every second of it, considering the fact that he drank 600,000 innocent people, killed thousands of others in cold blood, and fully intended to hunt down and kill every last human on Earth while savoring their terror and despair.
- The movie Sleepless in Seattle is based on this premise. Jonah wants his sad father to remarry, so the boy takes the initiative to call a radio psychiatrist, setting off the whole sequence of events.
- In the movie Gregory's Girl by Bill Forsyth, Gregory's younger sister Madeline is a classic example of this trope.
- In The Karate Kid Bobby says he can beat Daniel in a fair fight at the tournament without breaking the rules and probably could have. He's bigger, stronger, and has more experience with karate. Kreese, instead, orders him to cheat so Lawrence can fight Daniel in the finale for an easy victory. Despite the fact if Bobby won, his dojo would win either way.
- Terminator 2: Judgment Day: In a Deleted Scene, restored in the special edition, Sarah and John remove the T-800's chip, intending to reprogram him so he can learn human behavior. Sarah has other ideas and tries to smash the chip with a hammer, distrusting the T-800. John stops her, and in the ensuing argument, drops a line that prompts Sarah to give in:
John: Look, Mom, if I'm ever supposed to be this great military leader, maybe you should start listening to my leadership ideas once in a while. 'Cause if my own mother won't, how do you expect anyone else to?
- Avengers: Infinity War: As Tony and Peter argue inside the Q-ship, the latter comes up with the line that the former can't rebuff:
Peter Parker: You can't be a friendly neighborhood Spider-Man if there's no neighborhood.
- The Emperor's New Clothes climaxes when a child utters the obvious truth that the Emperor has no clothes.
- The Baudelaire Orphans repeatedly in A Series of Unfortunate Events.
- The Bible originated the expression, "Out of the Mouths of Babes" that relates to this trope.
- This is a recurring theme in the Deryni works generally; younger people are seen to question and doubt old ideas: the fears promulgated by the Church hierarchy and the received wisdom (untested) of the High Deryni Lords of the Camberian Council. Some of the younger people even act on their different notions of the proper and the just. In particular:
- Deryni Checkmate: During the meeting of the Curia on the Corwyn Interdict, Archbishop Corrigan (then Archbishop of Rhemuth and Loris's ally) reacted to the defiance of the younger Cardiel and his allies by "[throwing] up his hands in dismay. 'O Lord, deliver us from men with causes! Are we now to be schooled by our juniors?'"
- High Deryni: In a meeting of the Camberian Council, Tiercel deClaron (the youngest member) mounts an eloquent defence of Morgan and Duncan when two other members deride them for being half-breeds. Tiercel starts with the proposition that they should be sought out "on bended knee, begging them to share their great knowledge with us" (referring to the pair's rumoured rediscovery of Healing, a talent lost for some two centuries). He goes on to suggest, based on what they know of the powers, that being Deryni may be an all-or-nothing proposition like other traits. After a long silence, Barrett deLaney quietly says, "We are well instructed by our juniors."
- Talen from The Elenium has a knack for figuring out things before the adults.
- Gher from The Redemption of Althalus. He's not just The Smart Guy, he's a young smart guy.
- Wesley in Star Trek: The Next Generation had such occasions, then started doing it a little too often, leading to some fan backlash.
- Once the rest of the Power Rangers Turbo cast changed over, lone holdover Justin tended to be the first one to figure out what Divatox's Evil Plan of the Week was.
- Played for laughs in the Community episode "The Politics of Human Sexuality"; after some Wacky College Hijinx involving an attempt to break into the Dean's office to view a large fake penis in preparation for an STD Fair, the Dean forces Annie, Shirley and Britta into a meeting with the Greendale counsellor, who immediately picks up that Annie — who, although older than the typical example of the trope, is clearly the youngest, most naive and sheltered of the three — clearly has some hang-ups about saying the word 'penis'. After a very condescending reaction on the part of the counsellor, who attempts to passive-aggressively force Annie to say 'penis' in front of everyone, Annie angrily snaps and declares that she's actually okay with being sexually repressed, pointing out that maybe if a few more people were a bit more wary of embracing their sexuality like her, they wouldn't need to have an STD fair in the first place.
- In Sherlock, In "The Sign Of Three", Sherlock is frantically trying to work out who the murderer could be, having worked out that Major Sholto is being targeted, and Archie pipes up with his suggestion that it could be the "invisible man with the invisible knife", who tried to kill Bainbridge. He's right, and Sherlock uses this information to help him solve the case.
- World of Warcraft: Anduin Wrynn is calmer and more diplomatic than his father, which sometimes leads to this trope.
- Knights of the Old Republic: Mission is a snarky, teenaged Twi'lek street kid who looks up to the Player Character like an older sibling. She is also tied with Carth as having the highest Karma Meter score in the party. She will often argue against unfair or openly oppressive situations or encourage the player to be the nice guy.
- My Little Pony: Friendship Is Magic:
- In the episode "Bridle Gossip", Apple Bloom is the only one to assume that Zecora isn't evil, in contrast to the Mane 6 who are much older than her and guess Zecora is evil. Turns out Apple Bloom's assumption was correct all along.
- In "The Times They Are A Changeling", Spike befriends one of the titular creatures who would rather befriend ponies instead of feed on them. Though it's not unjustified of the ponies to refuse to believe a changeling could be good, considering their one and only interaction with them, Spike's insistence that Thorax is actually a good guy is ultimately proven right.
- The Simpsons. There are a lot of episodes where Lisa (as well as Bart and sometimes even Maggie) manages to come up with a solution where adults have failed. She is usually more intelligent than Homer as well.
- The protagonists of South Park tend to invoke this in episodes with An Aesop.