HUNGRY HUMAN HIPPOS Get some carpet dollies or champion scooter boards with handles and make this happen. You can use bungies or ropes to pull them back after they have collected as many balloons as possible.
Make a backyard bowling alley. Add food coloring to clear plastic bottles of water. Use party streamers as lane margins. Add glow sticks for night bowling. (These would make great outdoor table nightlights also with the glowsticks, gonna try it!