Sponges: Any kind will do. Look for cosmetic sponges,
kitchen sponges, pieces of foam in a variety of shapes and textures.
Tempera paints
Dishes for paint
PaperPour paint into the dishes so it is easy to dip the sponges.  Use scissors to cut the sponges into simple shapes: stars, hearts, trees, flowers, animals, letters of the alphabet, or whatever.  Pieces of sponge or foam can be torn into unusual shapes, too.

Dip one side of the sponge into the paint, and press firmly onto your paper.  Lift the sponge straight off the paper.  Sponge printing is especially effective when you repeat the images several times.  You can use it to create greeting cards, gift wrap paper, make pictures, picture frames or even to decorate tee shirts.  Use like a stencil to decorate your bedroom walls!  Use acrylic paints if you choose to paint on fabric or walls, so it is waterproof.

From the book Kids Create, Art & Craft Experiences for 3 to 9 Year Olds by Laurie Carlson