Verbier - we go every couple of years with the family.
Our kids are about the same age, we tend to hang out at the outdoor pool, go for big walks in the woods and do day trips to the mountain zoo, see the dogs at Grand St Bernard, drive up to the big dam for a scary look see over the edge and just generally hang out. The pool is great, where else can you splash around in 30c heat and look out at a glacier on the Italian border. Also, Verbier is a really lovely town, nice and compact but loads going on in the summer. All the bars and restaraunts open up again for the summer season (June-Sep I think) and you have the music festivals, show jumping etc etc. its all good if not cheap.
Riding wise I may well take my Ti456 next time, take the lift up and ride around the top or do some of the big tours from town. Are plenty of lovely single track trails you can go on with a hardtail too and the bikepark above town isnt all black-run madness, plenty of fantastic riding. I get up early, ride for a bit then go join the family....everyone is happy.