Arts and Craft kid-friendly product that can be dated back to probably the 50s.
Basically it's this sheet of cellaloid that you can draw and/or cut out shapes and images on that you bake in the oven at a low temperature (like 100 degrees F), and they shrink to about a quarter of their original size, as well as harden to a plastic-like product.
I hoped they took those off the market, because there were several "shrinkie-dink accidents" that we had, most of which involved the prodcut being able to break into a sharp point after the final point. Not to meantion the many chocking hazards we were able to produce because we didn't factor in the shrinking part.