The best choice out there for the Wii would be Big Brain Academy: Wii Degree. It's very kid friendly. You might also be familiar with Big Brain Academy for the Nintendo DS.
i don't think this game was made for the wii but if you have a ps2 you could try the game "buzz" its a gameshow game, like "who wants to be a millionaire?"
Thanks . I gather that there not more than 4/5 titles available in the market for wii edu games. Developers please note that parents will be more keen to get wii if more edu titles are available in addition to other games.