These were a big hit and the pictures they made are very pretty. To make the ice cubes, I filled a regular ice cube tray with water and squeezed a different color of washable tempera paint into each cube. Then I popped them in the freezer. When they were frozen, I gave each child a piece of white paper on a tray and two colored cubes of their choice.
They really enjoyed mixing the colors and feeling the ice cubes, especially when they got slippery.