With a teen and a tween boys here, I thought seriously on a 360 just recently. However, switching platforms at this time would have implied starting over with games and/or maintaining the wii and the games they still play with.
I preordered a deluxe wii u. And been pushing them to hold off on getting any new games. They noticed already FIFA will come out for Wii U and doesn't seem to be available for Wii, even though the other ones are out.
This way, the new titles will have the much better graphics but they'll continue to use the older wii titles.
Also, the controllers move forward as well - no need to invest in additional wii motes or nunchucks.