Wow, your lucky because lately there have been A LOT of kids games. :P
Wario Ware maybe a little too fast for a 4 year old, probably not for a 7 year old though. Wii Sports is great but I'm sure you already have that. There are a lot of movie games like Ice Age, Open Season, Cars, and stuff like that.
Super Monkey Ball also might be something you consider. I haven't played it myself, but watching it being played seems like it might be good for a 6 or 7 year old.