If you haven't heard of this idea before or have not tried it yet with your kids, add it to your list of crafts to do! It's fun and kids love the end result.
All you do is have your kids draw a picture with crayons on a piece of paper. Then use watercolors to paint over the crayon. The crayon will resist the watercolor paint, but the rest of the blank paper will be filled in with the paint.
It comes out looking very cool and a picture worthy of framing.