S.T.
They are all very hot. The water ones are a whole lot more comfortable. But little kids don't seem to feel the heat the way we adults do. I do suggest you station an adult at the door to help the kids get in and out - that seems to be a place when there are a lot of falls. If it's possible put it in the shade. If there are going to be little kids and big kids try to keep the big kids and little kids in separate "sessions". The bigger kids don't realize how aggressive they can be and how little the little kids are. if a 25 lb kid bumps into a 40 lb kid it's not so bad. But bumping into a 85 lb kid is another story.
Good luck mama!