There is a Root RPG based on the PbtA system. It's a fiction first system which means it's quite flexible and you can run all kind of adventures in it not only combat ones. The book also uses the same art style as the boardgame for the illustrations.
Another option is Mouseguard. It's based of a series of comic books aimed at kids and it has mice trying to survive and fight against predators (snakes, owls that sort of stuff). It uses as simpler Burning Wheel system and it also encourages storytelling with each character having beliefs and goals that influence their actions. The art is also the same as the comics so it's pretty cool if your kid likes mice with swords and axes.
Hope you have multiple attacks. That's a lot of boars.