The faster it vibrates, the higher the pitch of the sound it produces. Try using a balloon to demonstrate how the death's-head moth produces sound. Hold the neck of the balloon between the first fingers and thumbs of both hands. Slowly stretch the neck of the balloon sideways as far as possible to form a narrow opening which lets the air out slowly. Only male crickets chirp, but both sexes have organs for hearing located on their front legs, just below their knees.
Males chirp to attract females and to warn other males away.
A great classroom pet might be the Madagascar hissing roach. Reassure them that the roaches are harmless, and allow them some time to get used to the idea of actually handling the roaches. Most kids will soon overcome their initial uneasiness and learn how to handle the roaches with confidence. The roaches may stop hissing when they get used to being handled by the kids. If this happens, avoid handling the roaches for a while.