Have you tried playing with water beads yet? They are SO fun! You can buy these almost anywhere now (Michaels, Walmart, Oriental Trading). They come in a small package and you put them in water to watch them grow. You control the size by how much water you put in. They are slimy, they bounce, and they are so fun to scoop and pour.
I put them outside in the sand table because they were getting away from us in the house.