[Quo]

Marvel Ultimate Alliance is pretty fun for co-op with kids. My wife cringed at a couple of cut scenes and stuff, but overall it's tame.

Lego Batman and Lego Indiana Jones are both supposedly slated for release next year if I remember right. Those are great games for kids.

If he likes Star Wars, try Star Wars Battlefront 2 and play split-screen co-op on Easy. It's a great way to introduce them to FPS's. My son loved it and still plays it with his friends some.