N.G.
We LOVE LOVE LOVE our Nintendo DS (we have two), and Cheyenne has been playing on it since she was 3, and Natalie plays with it too. They have games for DS for all ages.
Nat is getting a MobiGo for Christmas. We've done the Leapster thing, and I was so disappointed with the thing because the touch-screen broke after three months. Cheyenne had a friend with the same leapster and her touch-screen broke after three months too. Calling leapster is futile, they don't care, and don't stand by their products. They refused any help at all. I read tons of on-line reviews of the leapster systems, and this seems to be a regularity across the board.
MobiGo, on the other hand, got great reviews.