>>96335416
Mouse Guard is an RPG based on the comic series by the same name. The comic is by David Petersen, and I really recommend it. It's not strictly a kid's comic, but it can be absolutely enjoyed by them too and doesn't have anything sexual or overly violent.
The game is by Luke Crane and is based on a simplified version of his Burning Wheel system. The players take up the role of Guardmice: members of an order that dedicates itself to protecting the Mouse Territories from predators, the weather and evil mice. It's a really interesting ruleset, and it's probably one of my favourites, but it's pretty crunchy, sometimes a bit too much for it's own good, so I wouldn't recommend to a small child, although an 11 or 12 year-old should have too many issues playing it. It does heavily depend on the child in question, of course: a friend of mine's brother GM'd Pathfinder games to his friends since when he was 10. The rulebook is clearly written with the assumption that's it's going to be read by a younger audience, but I think that a small child is gonna be a bit overwhelmed by all the rules. The art is by David Petersen, and it is gorgeous.

Mausritter is an OSR-esque game where you play mice adventures in the modern world. There's all the classic Dungeon Crawling package: Ancient ruins inhabited by mysterious cults, evil wizards and their towers, hex maps and lethality. There are also all the problems that stem from being a small mouse in a world populated by humans.
It's extremely rules-light, and character creation is completely random. The Inventory system is probably my favourite part of the game. It's simple enough that no kid should have big problems playing it, but since dying is very easy, again it depends on the child.