I posted the same question on Facebook, and the majority there say Xbox. I have a Wii, and the boys always ask me to bring it when I visit, and they certainly have a lot of fun playing it. But, I'm leaning towards the Xbox with Kinect only because it can be played similar to the Wii, and as they get older, I think they'll appreciate it more in the long run.

M60s
VP150
QS8s
Marantz SR6003
Samsung LN52B550
Oppo DV-980H
Insignia NS-WBRDVD