Make a reed musical instrument from a drinking straw and learn some things about the science of sound.
When I lived in Bangladesh (in South Asia, next to India) I was intrigued as much by the musical instrument the snake charmers played as I was by the snakes.
I was so taken with the snake charmer's instrument that I bought one. How could an instrument made only of bamboo and a hollow gourd--held together with wax--produce such an exotic sound? I set about some research and discovered the motley reed family of instruments. Saxophones, harmonicas, accordions, bagpipes, clarinets, snake charmer’s pipes and even duck calls (ergo the attention-getting name "snake charmer's duck call") all use "reeds" to make music. And so can you!
This is a great project to do with groups of kids. It only takes scissors and a straw, and with practice you can play a recognizable tune on it.