Footie Pajama Pants

footie pajama
(Footie pajamas) The blanket sleeper (also known by many other synonyms and trade names) such as is a type of especially warm sleeping garment worn primarily during the winter in the United States and Canada. The garment is worn especially by infants and young children.

pants
(pant) the noise made by a short puff of steam (as from an engine)
Underpants
Rubbish; nonsense
(pant) breathe noisily, as when one is exhausted; "The runners reached the finish line, panting heavily"
Trousers
bloomers: underpants worn by women; "she was afraid that her bloomers might have been showing"