Heh, you and your Nephew are gonna have a blast with Mario Kart Wii. If you thoroughly enjoy the aged Mario Kart 64 still, MK Wii should be quite the fun upgrade.
To be honest, after playing MK Wii I couldn't go back to playing 64. MKW is just so much better, lol. Smoother controls, the tracks are crazier and more fun than before (along with a ton of the old tracks with upgraded graphics), and all that jazz.