So this is pretty fun, maybe not as much as flinging a brush around but, lets face it, we don't want to clean paint off the ceiling.
You will need:
A tall can - like one used for bread crumbs
3-4 small rocks or marbles
Cut or fold the paper to fit inside the can. put 1 nickel sized glob of each color desired. drop in rocks/marbles and put on the lid. now let your kiddo shake/wiggle/roll the can. When they are worn out dump out the marbles and take the paper out to dry.