Have you ever heard of Paper Squishies?
They are a fun way for kids to create their own squishy. All you need is paper, crayons/markers/colored pencil, clear packing tape, and something to stuff it with (lots of options..plastic bags is a great one!!). It is best to keep them a round/circle type shape (just trust me!!). You can theme them any way you like, and can bring in a number of art concepts to amp this project up!
You will see some of the other ones teachers made in the group shots (where I took pics of all their work they created during the week).