We've been HOT in Texas this summer and have had to keep most of our activities indoors. One afternoon my 3-year-old and I made a tray of rainbow ice cubes, and they were a huge hit! I just filled up a small plastic tea pot with water for her to fill each cube, then we squeezed one small drop of food coloring into each one. We stuck to mainly primary colors. She used a toothpick to stir each cube.
Once these were frozen, the possibilities are absolutely endless. My daughter had so much fun mixing a couple of cubes into a Sprite to see what color it would turn. I always cool her oatmeal with 2 ice cubes after it's cooked, so I used a blue and a red one. As she stirred and her oatmeal turned purple, she was thrilled. You can also stick a toothpick in these as they're freezing to use as a handle. Then, when they're frozen, the kids can use the toothpick to hold it to paint on paper outside. They could also use the colored cubes as a sensory activity floating in water in the sink.
Hope you have as much fun with these as we did!