Teams race to blow up balloons until they explode.
Balloons and bicycle tire pumps.
Divide into teams of two. Buy a couple of balloon pumps or bike pumps and attach a balloon to the nozzle. The kids have to pump the pumps or bounce up and down on the pumps until the balloon bursts. The first to burst wins. If you only have two pumps you can set up a small tournament single elimination style until one team wins.