All I did was took some Pure Silk women's shaving cream (which I got a while back with coupons for all of $0.15) but any shaving cream that foams white will work (I think you can get it at Walmart for $1), and sprayed it in the wells of a muffin tin. Then I took some of Grant's Crayola washable paint and put maybe a teaspoon in each and mixed it together. I found an old paintbrush, that will now be his bathtub paint brush, and let him go to town.
I think the "recipe" on the original website used food coloring instead of washable paint but after cleaning up the cool whip we played with and seeing the food coloring stain Grant's entire arm, I was afraid it may also stain the walls of the tub. The last thing I wanted was to have to scrub the tub walls any more than I do already.
This is definitely an activity we will do again. He was so excited about his painting he begged me to take a picture so he could show Daddy. The best part for me, other than seeing how much fun he had, was the clean-up was as simple as wiping it off with a wet washcloth.
This could also be an activity for playing outside. You could take a white shower curtain from the Dollar Tree, your shaving cream paint, and some sponge brushes and let the kids have at it. Then just hose them and the shower curtain off, and hang it up to dry for another day. Or leave the shaving cream on the shower curtain and use it as a foamy slip and slide.