Wii is very fun
The best games for wii that are kid friendly (almost all wii games are kid friendly, but still I like to double check) in my opinion are:
super mario wii
super smash brothers (a little bit violent but very cartoony, perfect for my 9 and 11 year old, sometimes I play with them and it is a blast!)
mario cart wii
wii sports
wii fit (I like to play this and the kids get a kick out of the balance games)