I wouldn't buy too many til you see if you need them. I have several pairs and never used them (my daughter is 5 weeks) she never scratched herself and she loves touching her face and putting her fingers in her mouth, those mittens would piss her off!
I used them all the time with my last
they get all sorts of spit on them and fun stuff of that sort lol so Id get like four pairs
We didn't use them with our first. We sometimes would fold the "mittens" over on the sleepers that were built in.
I didn't even think of that what size would I need 0-6 months
get the mittens with the onies at Carter's
I never used them