A lot of people younger than me (I'm 40) have never heard of Colorforms. If you don't know what they were, they were these scenes from cartoons mainly, that had a waxed surface. There was a sheet of rubbery plastic that was of the characters themselves, usually in more than one pose, as well as every day items like clothes, furniture, etc. The pieces didn't permanently stick, but had an attachment kind of like static window pictures. So you were able to make scene after scene, changing it to what you wanted. There were all kinds of them. There were Charlie Brown, Marvel and DC superheroes, Tom and Jerry, Muppets, and Wizard of Oz just to name a few. I loved them! They probably wouldn't survive in today's microchip society, but they were great back in the day.
If I'm not wrong they are still coming up with new Colorforms! I think that there are some of Spongebob Squarepants, being a 2000s cartoon I think it speaks for the popularity of the toy. Although in this day and age I agree that it might be more for adult collectors than for kids, since the same experience can easily be derived from an electronic tablet.
We still have colorforms and if you can check Amazon you'd find lots and lots of them, some pretty old ones are listed as well.