Mosaics are pictures made from tiny tiles. Usually these are ceramic or glass squares. For my students, I cut up colored foam for an inexpensive alternative. Each student spray painted a piece of cardboard as a backing and used Elmer's glue to adhere the tiles.
This is a great project for children to gain fine motor skills and learn that many small things add up to make a big difference. There were some students who cut the foam in different sizes and shapes if they felt their image required it. And for students, who are blind, we left large spaces without tile, so that they would be able to feel the shape of the image without the confusion of having the background and foreground filled with texture. Maybe we'll try using ceramic tiles and grout in the future, but I found that this was a great way to introduce mosaics to children.