WARNING: The following activity was extremely messy, i.e. I now have paint on my ceiling! If you are not as adventurous (crazy) as I am, I suggest trying this one outside with Street Paints.
For this project I bought a couple of cheap fly swatters, poured some paint in a tray (of course they had to be Black Light Paintings, because everything is more fun when it glows in the dark!) and let the girls swat their little hearts out!
CLEAN-UP TIPS: Since we were in the bathroom, I just put them in the tub, and cleaned up the mess while they played. Washable paints wipe up very easily, especially if you do it while they are still wet. Plus, just think how clean your bathroom will be when your done!