We've been wanting to try this all summer, but we just now made time for it. I filled an ice cube tray with water and added washable poster paints. We only have red, blue, and yellow, so we had a lesson on mixing colors. We mixed the colors with toothpicks and then froze the cubes.
Frozen Ice Cube Paints
I left the toothpicks in four of the cubes to see if they would work for handles while painting. The toothpicks just broke- don't try it! After the cubes froze, we took them outside and had a blast painting with them!