This is a simple circuit. Power>MakeyMakeyBit>3Bananas and a Spoon Plus Scratch.
I created a neat little Scratch program called Banana Piano which plays a beat constantly and allows the user to play random notes on 3 different instruments using the space key and left and right arrows. I also made as much color and graphic change as possible to attract little (and big) kids. The wonderful thing is you can use the MakeyMakeyBit to input these three keys using any conductive surface (in this case bananas).
You can also remix the basic program any way you want, different instruments, different graphics/colors/etc.
And of course you're not limited to bananas!
My youtube embed doesn't seem to be working below, here's the direct link to the video of the project:https://youtu.be/8D4JgkU6JWU