Classic play has a really easy way to create a musical instrument using plastic straws and tape to create a diy pan flute. The trick is cutting the straws to the sounds you want. She recommends cutting each straw an inch apart.
Good for ages 5 and up.
Get the instructions here:
http://www.classic-play.com/straw-pan-flute/
Deceptively educational has a tutorial as well.
http://deceptivelyeducational.blogspot.com/2012/04/making-magic-drinking-straw-flute.html