Make a Diet Coke Geyser with Mentos
Buy a fresh 2-liter of Diet Coke and a pack of Mentos. Have your child tape a tube to the opening of the soda and position the pack of Mentos directly above. Drop half of the pack of Mentos down the tube and tell your kid to run like crazy. The geyser will soak everything in sight due to the release of carbon dioxide. For more fun, drop the other ½ of the pack!