So here is how you make it:
Put some popcorn kernels (or dried beans) in a plastic bottle. It is also a good idea to clean this bottle well before handing it to you kid.
This happens to be an empty pop bottle that I obtained from a table at the public library (free).
So it really cost us almost nothing.
I can also envision some creative folks bedazzling the bottle up in ways to make it even more engaging for their children. My wife suggested adding a little bit of multiple dry food sources to make it more comfortable. I opt for the most simple route usually :)
Thanks for reading,