Ahead of time you will need to dye the rice in the seven rainbow colors. Do this by placing a few handfuls of rice and a drop of a different food coloring in each of 7 plastic bags. Then shake the bags. Spread the rice out to dry on paper towels.
Have the children draw rainbow shapes on paper. Show them how to use a brush to spread a thin layer of glue over one band of the rainbow and then sprinkle a thin layer of rice over the glued area. Now let the children glue-and-sprinkle to make their own rice rainbows, following the color order that they learned.