Children create a circle including the group leader.
When the leader raises their index finger, everyone begins to clap using only their index fingers. As the leader raises more fingers the clapping begins to go faster and louder. When the leader has used all fingers, leader decreases one by one the number of fingers raised so the noise eventually stops.
To make the game more interesting, have the leader raise fingers slowly, faster and variate between all up, all down, some up and some down.