Crayon hot rocks: If you have not done this yet, you need to. Simply warm up the rocks in the oven (I did 220 for 10 minutes), then put them on a stack of newspapers (or something else you don't care if it gets crayon in it). Just remind them it is hot.
Simple Straw Airplane Sure paper airplanes are fun, but your kids will love how well this simple straw plane will soar across the room! Instructions for Simple Straw Airplane Compare with a regular paper plane and chart results
Paint that grows. Mix 1 cup flour, 3 tsp baking powder, 1 tsp salt, and enough water to make consistency of pancake batter. add food coloring, paint and then pop paper in microwave for seconds and watch the paint puff up and grow.