Kids don’t need to use any sharp tools when they create designs on flat foam sheets. Just draw on the surface with a pencil or ball-point pen to make embossed lines. A regular printmaking brayer is then used to roll a thin layer of water-soluble printing ink over the foam, and a piece of construction paper is laid on top and pressed firmly with fingertips (taking care not to wiggle the paper). Many prints can be made from a single foam block design.
Flat pieces of foam can be cut from many kinds of packages, from pizza boxes to the hinged “take home” containers used by many restaurants. It’s a great way to reuse/recycle in your art curriculum.