Go to a traffic free, snow sure resort. We liked Saas Fee and stayed at the Alphuebel . It has its own creche included in the price , under 6 's stay and eat free, early kids' tea (optional), electrobus to the slopes(which to be fair is otherwise about a 15 min walk) and the kids can be brought from the creche to meet you at the end of skischool lessons. Indoor pool in resort and lots of other things to do if you fancy a break from skiing. There are reviews of it and other tried and tested's here
La plagne( BELLE PLAGNE)is one of the prettiest french resorts. More like austria but dont go to la plagne 1800 or plagne centre it is concrete. Flaine is good for ski schools and beginners but it is not the best design in terms of the concrete buildings. Practical as everyone tends to meet in the same place for the ski schools and the nursery is really central. Mine learnt in flaine aged 3 and 5 ,they loved the ski school there. Supermarkets are well stocked and good bakery.
In austria....Zell am see is good for ski school and runs are more suitable for beginners. Zell am Ziller is good too