Go get some and play with it. It's insane. If you mush it, you can mold it like play-doh, but start spreading it out (to let air mix in) and it crumbles like sand. It never dries out, and it's not too tough to clean up.
I like Sands Alive, that one is also anti-bacterial... so if a sick kid plays with it, other kids won't get sick.
DO it