Whatever boots you buy, make sure they are big. That way they can wear multiple pairs of socks and/or add foor warmers.
Get the gloves that are also mittens. Mittens keep their fingers warmer. Some have a slot for putting a hand warmer in them.
I used snow gear when starting. If wading was needed, I carried my boys or you can use a decoy sled to pull them around.
If hunting in water, get them a flotation deviceThick coveralls work great for kiddos. Warmth is way more important that waterproof

. If the kids are warm, I could easily just throw a big thin waterproof jacket or poncho over the warm clothes.
PS - lots of snacks and even their own duck call are helpful. Let them pull the jerk cord if using one
