With chalk paint or even just water! Washable Chalk Paint for Kids. Peyton and Handyn did this today and they had fun for hours. My backyard, fence, concrete, windows, and even the dogs are very colorful. Recommend to anyone with young kiddos.
Feed the Elephant: (Charlie painted this on a washing machine box and used a dryer vent for the trunk.) The kids would place peanuts in the trunk to "feed the elephant" and raise the trunk until the peanuts dropped inside.