Balloon Rocket Race

Thread a length of string through a straw and stretch it tight between two fixed points for each racer.

Inflate a balloon without tying it off and tape it securely to the straw, facing the balloon's opening toward the starting end.

Hold the balloon's neck closed until every racer is ready at the starting line.

Release all balloons at the same time, letting the escaping air rocket each straw along its string.

The balloon that reaches the far end of its string first wins the race.