I recommend one soft sided, water resistant, cold resistant duffel bag per skier – yep, even the kids.
A duffel that is well-marked and has a checklist packed right in it is invaluable.
As soon as the kids can read, they can pack their own duffel bags with the enclosed checklist.
Select duffel bags large enough to hold items on your packing list (see link below). Use duffel bags ONLY for ski gear. When packing for a ski trip, especially if it requires air travel, include street clothing and toiletries in a separate bag.