For the xbox 360, whats a really fun game that is suitable for children.?

I have my little cousins (they are about from 9 to 11 years old) that come over almost every weekend to play. The only thing I can't let them do is play on my xbox 360 because i only have games that have violence, blood, gore etc. Games like gears of war, saints row, and rainbow six vegas. Their parents wont tolerate that stuff, so what's a game thats really fun that is suitable for the youngsters.