Steppers are an interesting music controller designed for 5-year olds:

As a group, we hoped to make a toy that not only encouraged physical activity, but that also acted a clear and direct musical interface.

Steppers transform walking, dancing, running, and jumping into a unique and dynamic activity, allowing the user to express themselves audibly through their movements.

The shoes contain force sensors, which communicate with a MAX/MSP program.

Here’s video of the Steppers in use: