In most instances I would say that sponge painting does not excite me very much. It gets on fingers and the spongy prints make me think of a home decorating attempt gone bad. But I discovered that a sponge as a vehicle for printing can be a pretty cool thing. We used ours as gift wrap.
You need paper, a sponge cut into the shape you want to use, tempera paint, squeeze bottles with a small opening, a printing plate (I used a plastic yogurt lid).
Squirt the paint on the printing plate. Press sponge onto paint. Print. Repeat.