Balloon Rockets - I've done this in several science camps I've conducted. Kids have fun with it. But, when the balloon deflates it may fall off the straw because it's surface area changes - another good thing to show and explain to kids.
DIY Catapults for Kids - Coffee Cups and Crayons Awesome STEM Activity for Kids--Make a Craft Stick Catapult using wooden craft sticks, paint and pom poms! If you absolutely love arts and crafts you actually will enjoy our website!