One Piece Suits
These will probably come back into fashion. OK, unlikely, but weirder things have happened. Great for keeping wind and snow out. Unequalled practicality on a powder day. You will not pick up.
Can be very good for little kids (1-5 or 6 yo) as you don't have to worry about them getting snow down their pants and up their backs. Will keep them warmer and dryer. Only downside is you need a bit more effort for them to go to the toilet but 3yo + can pick that up pretty quickly and the benefits outweigh the downsides here. If young kids are wearing them to ski school/kids club put shorts on under them as they will probably want to take them off when inside for play/lunch etc.