I just finished doing this with my little ones. It was fun and easy. Now it's drying and later I will use it to make "eye spy" bottles. But, I like the idea of the "discovery center" on this blog too! :-)
Need plastic bottle 1/3 filled with water add blue food coloring. Add oil to fill the bottle (oil and water dont mix so it gives you waves!) You can even add sand,glitter,plastic fish, seashells whatever to make it look like an ocean! Pretty cool I want to try this!