"No need for thick (or multiple) socks - kids do better with one pair of thin socks. They should be snug enough to avoid wrinkles and tall enough to reach well above the height of the boot. You might need to reach in there a few times during the ski day and pull the socks up again. This smooths out the wrinkles and improves comfort. Stay away from cotton socks! Kids'll be warmer and drier with wool or synthetic socks."