Mikel, I don't know what kind of 4-year-olds you're hanging around with, but some of those games are way beyond most of them. Call of Duty???
Then again, the OP's 4-year-old is 7 now, so those titles could work. :)
For a 4-year-old, try Wii Music. It's not really a game, but it is pretty neat for young kids to play around with.
The Wii version of Transformers: Revenge of the Fallen has a special 2-player mode where one player controls a character normally, while the other controls a "drone helper" and only has to point and shoot. It's pretty good for a parent to play together with a youngster.