Zelda MatildaChildren Toddlers Infant and Baby Mittens - Thinsulate Winter Waterproof Gloves

Are these completely waterproof? I'm taking my son skiing/tubing in November and don't want his hands to freeze up

Do these run true to size? I have a 21 month old and am torn between the 1-2 and 2-3 year size.

Is this product good for health?

What material is the inside??