A musical xylophone is fun - if he can take glass bottles to school. Fill them different amounts so they play a scale (5 notes is good but 8 notes for a whole octave is more impressive.) If he can't take bottles to school, can he borrow drinking glasses from the dining room? If you have a piece of bamboo, get an adult to cut out grooves in it. Scrape across the grooves with a thin stick. Hey presto, a home-made guiro! Something simpler would be filling plastic bottles with different substances, such as rice, small pasta, stones etc. to make various marracas (shakers).