If you tell a kid a fart joke, he'll start to laugh. He'll laugh so hard that he toots. Then, that reminds him of what made him laugh in the first place and it makes him laugh all over again, until he toots, which makes will make him laugh...
I've discovered the secret to perpetual motion. Nothing kills with an audience of five year olds like fart jokes. Nothing.
Harry Truman's Vice President, Alben Barkley once said that the best audience is, intelligence, well-educated, and a little drunk."
For five year olds, the key is gassy. If that's your crowd, ply them with beans.