@loren I would use "roly poly" for a roll on the ground, whereas I think a somersault can be in the air?
We avoid confusion with the woodlouse in the traditional British way of making up 100 other weird-ass names for that. (Where my wife grew up they are called cheesy-bobs.)
@loren
My knowledge is 30+ years old - a roly poly is a forward roll? A somersault being the much more difficult thing with arms stretched out.
British English is also very regional, East Midlands / Derbyshire in my case. One word used in the school playground was 'scraiting', or 'crying' - years later I discovered it to be a leftover from the 9th-10th century Norse / Viking Danelaw.
(My technique for discovering that words aren't known in American English is when US colleagues start looking at me strangely, then have to ask what the heck I'm rabbiting on about...)