Oh god, just about every piece of media ever, honestly.
Most anime and JRPGs, of course. Plenty of WRPGs (Even if the MC isn't young, they almost always have bg NPCs who'd fit). Lots of superheroes/sidekicks (Spiderman, comics Kid!Loki, Young Avengers, etc.). Ender's Game. ASOIAF. Most YA lit (Harry Potter, Hunger Games, Lord of the Flies, etc.). Plenty of TV shows and cartoons (Buffy, Walking Dead, AtLA, etc.)
Plus a lot of times this is the origin story for a now-adult character.
no subject
Most anime and JRPGs, of course. Plenty of WRPGs (Even if the MC isn't young, they almost always have bg NPCs who'd fit). Lots of superheroes/sidekicks (Spiderman, comics Kid!Loki, Young Avengers, etc.). Ender's Game. ASOIAF. Most YA lit (Harry Potter, Hunger Games, Lord of the Flies, etc.). Plenty of TV shows and cartoons (Buffy, Walking Dead, AtLA, etc.)
Plus a lot of times this is the origin story for a now-adult character.