It’s lovely, which is why I bought a place there and go back every winter and summer.
Lots to do for grown ups, a bit less for the smaller ones. There are the ubiquitous donkey rides etc, but for me one of the attractions of the place is being able to take a chairlift up, walk along a ridge, and take the lift down – ideal for the kids. You’re obviously within easy distance of Chamonix (take the railway up to the glacier, walk inside it etc), there are several aeriel walkways (rope-things) which at the lowest level would be fine for your young ‘un, there’s Lac Montriond, the summer sledge-run (fantastic!), a new swimming pool to be completed for next summer…loads of stuff. Not sure you’d be able to do even the most gentle of the white-water rafting-type activities though.
Whilst there are a fair number of Vaderesque characters shredding rad to the power of max (sadly, I’m one of them), they don’t take over the town, and the lift queues for non-riders are very short.