[quote name='kilm']
Maybe this question would be better served in the Wii forums
[/QUOTE]
Agreed - I just moved it there.
[quote name='DarkSageRK']All Wii games are aimed at the three-year-old demographic, so you should be good to go with any of them.[/QUOTE]
Oh, yeah, sure, like Resident Evil 4, or maybe Manhunt 2? Or perhaps Madworld or No More Heroes?
Seriously, though, you may want to consider Wii Music. It isn't the greatest game but I could see a 3 year-old having fun making the sounds. It isn't really a game though - however, you might be able to find it nice and cheap at Blockbuster ($9.99 for a used copy and they often come complete and in excellent condition). I got one that I was thinking of letting my 2 year-old play around with.
3 is definitely too young for NSMB or Mario Galaxy, though they would probably have fun just running Mario around in SMG. Same with Mario Kart - not great as a game for a 3 year-old, but good for messin' around.