We did a two-part lesson on the science of sound and music.
In the first part, we gave the kids plastic bottles and let them experiment with how to make different sounds with the bottles depending on how large the bottle was and how much liquid was in the bottle. The lesson was adapted from this lesson from the Dallas Symphony Orchestra (lots more lesson plans available on their website!) We explained about sound vibrations and the ear drum, and did a simple experiment similar to this one:
For the berimbaus we used dowels and hat the children use screwdrivers to put a small screw on the same side at each end. Then the children used fishing line to stretch between the two screws, but left enough room to put a plastic bottle between the dowel and the string. They then used a chop stick to pluck at the instrument. It worked very well!
More on this here http://www.nyphilkids.org/lab/make_berimbao.html
The finger pianos started with a piece of plywood cut to 6″ by 6″. The children cut large bobby pins in half and stapled them to the plywood at different spots along the bobby pins (further up made a higher sound). They bent the bobby pins up a bit to make it easier to play. These also worked very well, and if you put them on top of a cardboard box, the sound could resonate a little louder.
More on this here http://www.nyphilkids.org/lab/make_fingerpiano.html
Overall, these were really fun for everyone and a huge success! I hope you try it at home or in your co-op or homeschool group!