Here is my plan for World Thereminization...
A child's toy theremin...not too loud, not too irritating of a tone, batteries that last a long time, or are rechargeable.
Perhaps a deluxe version could play a series of two or three notes, and the tyke could try to match the pitch. Or it could have a button on the top. The child could hit the button, the toy would emit a tone, and the student could try to match the tone by moving his hands around the theremin. Or the unit could slowly play a song, and the child could try to follow it.
Little children (I do mean little), just love it when things respond to them.
I think a 3 year-old could be captivated by something like this.
Thereminless