Do I need to have a "land" area for my tadpoles?

I've recently acquired some tadpoles and I'm worried that I'm suffocating them or something. I know they're supposed to still have gills but some are starting to sprout legs and one of them keeps jumping up out of the water like he's trying to get air. Currently all I have is a steep, bumpy, slippery plastic rock-thing with like three spots of a square centimeter out of the water. Should I add a better place for them to be on land or are they still good?