It's super simple - 1T cornstarch
4-6 pumps of baby shampoo,
2-3 drops of food coloring
1-2tsps of water.
I mixed mine in a cupcake tin and it worked perfectly. Aria rested it on her legs whlile she painted the walls and herself!
She had a ton of fun and loved all the bubbles in the water at the end! Clean up was a synch and she came out squeaky clean :).