I want to make a

I am wanting to put it in one of those plastic kiddie pools. And a lt of it. Also, any other ideas for fun and gross things to do would be appriciated. We are going to have them toss raw spaghetti at each other, raw egg races, human sundaes, water gun fight.
An easy one to do is to mix water and cornstarch. The mixture has the property of allowing your hand through it if you put it in slowly, or to be hard and crumbly if you sock it. We used to make it and sell it during high school festivals and it was really popular. There is also a several other mixtures. There is a glue-based mixture which relies on a combination of Elmer