I cannot recommend this "science project" enough. Elliott (and I) had so much fun playing with this. It is impossible to keep your hands off of the gloop. Cornstarch does some crazy things when mixed with water. When sitting in the bowl, gloop looks liquidy (Yes, I know that's not a word, thank you, spell check.) but when you touch it, it's actually kind of rubbery. Pick it up and (the coolest part!) it forms into a kind of slime and drips back into the bowl. Roll it in your hand and it turns powdery. All things to keep in mind when trying to teach your kids about textures. Try this one! You will not regret it.
Gloop is fairly easy to clean up since any stray pieces turn powdery (so cool!) and can be swept up. However, I do suggest doing this one on a hard surface and not a carpet.
We stored our gloop in a Tupperware dish for about a week until it started to smell a little funky.
I don't know if I will ever again be able to eat any recipe that uses cornstarch.