Basel has a cricket club: http://www.baselcricket.ch/
, although I guess getting towards the end of the season.
There's the rugby club which has a lot of expats, but I don't know how much is geared towards children.
What school are you putting them into? If going local, then it will be harder to integrate into the expat community as when I look back most of the English-speaking friends we made were through organisations like the BCT (http://www.baselchildrenstrust.ch/
) - this could be an option as well.