Bit trivial, but take spare mittens, they will play in the snow and get their mittens wet, I also took one of those peggy things that I use for knickers at home to hang damp mittens and socks on overnight.
As you've already booked not all of this will help you as some of the big decisions will be made, however ... we just went skiing with our 1 year old and had a great time. Obviously he wasn't on the slopes although I guess yours could be.
Catered chalet - made life a whole lot easier not to have to worry about feeding ourselves, or worrying what to make DS. Also meant we could relax in the evening and enjoy the vino. More expensive but deffo worth it.
Pick a resort with other things to do than ski so you can vary what the DCs are doing.
Split your days to share childcare. Or hire a nanny at least some of the time.
Take the DCs up the mountain even if they're not skiing - pick a decent lift (telecabin or bubble) which takes you to a mountain restaurant.
Booked a ski holiday with DCs (4&3) in a couple of weeks. Please can you give me your top tips and advice, things you have learned, what not to do, what to do, how to make the most of the holiday etc Thank you in advance!