looks to me as if these are just pyjamas, only they seem to be far more used for children, which makes me think, they are one-piece pyjamas.

"I remember sitting in my one piece, feetie pajamas watching the Grinch steal Christmas every Christmas eve."

http://www.epinions.com/mvie-review-5042-A973A73-3A3630E2-pr...

There are plenty of references on the web to feetie pajamas, I suspect clear could have something to do with the colour...