Most of the games for the Nintendo Wii require you to follow on-screen instructions and perform some (more or less) precise movements. Keep in mind that the Wii is just the platform, there are many games for the Wii, some that are appropriate for children and some that aren't. Of all the systems currently out, though, the Wii has the most aimed for children.

I Would say a game like wii sports could be equally fun for you six year old kid as it could be for you. A six year old is capable of doing somewhat advanced puzzles and solve easy math problems so he will be likely to learn how to control the wii games, though you might want to instruct him. After all six year olds can ride a two wheeled bike can't they? :)

Kids these days are getting more involved in the technology scene and at a younger age. It will just depend on which games you buy for your 6 year old.