Thanks to Melanie for contributing this idea! She wrote:
Right now my boys are huge into Pokemon, the original series
(that's what we get for getting videos from the public library that
are 10 years old). They love to pick out their pokemon and color them
themselves and cut them out and battle with them. I made Poke balls
for them to keep them in, thought I'd send along a picture. It's a
paper pocket made from a whole white circle and a half red circle,
with the black stripe glued to the red half. Melanie