Hook a bubble machine up to a switch. The child using the switch makes the bubbles, and it is everyone else's job to catch and pop them as fast as they can. Say, "hurry, hurry!" The child using the switch will have his hand slide off intermittently and may learn to wait till the other kids are begging him to make more! (No one else has permission to run the machine). You can find bubble machines at Target. They can be used with a battery interrupter.
