Mosaic Project for Kids
Why not try making a mosaic? You can make a simple mosaic just with black and white pebbles, which you can get at any gardening store. You could set them in plaster of paris, or in cement the way the Romans did it.
Or, in a classroom, you might want to just cut out lots of little squares of colored paper, and assemble them into mosaics with glue. For the best results, make sure to have some light red and some darker red, and some light blue and some darker blue, and so on, so that you can do some shading. The pieces should be about 1 /4 inch (1/2 cm) square. Look at a lot of pictures of mosaics first so you can see how they do it (there are many on this site).