I'm not sure how to categorize this one, but it's a fun concoction to make and play with. It'll definitely be part of our slime day at the library, even if it's not actually a slime!
Pour some corn starch into a bowl. Squirt in some shaving cream, about the same amount as you have corn starch. You're just eyeballing it. Quantities aren't terribly important and you can always adjust amounts as you go along.
Dive in with your hands and start squishing it all together - a very tactile experience!
It will become a soft clay that you can mold into all kinds of shapes. As time goes on, the clay will get stiffer.
So much fun!!