Start with a box of white cake mix. Make it according to the directions on the box. Separate it into 6 bowls. Get out some plain old food coloring and get to work. Make the kids count it out for you.
Put the kids to work and mix until all one color.
Starting with purple, drop a heaping tablespoon of batter into a paper lined muffin tin. Smooth it out a bit before you add the next color. Repeat until you get to through all of the colors. Spread the red evenly over the top so that it looks like the cupcake is only red (there will be a nice surprise when they take a bite). Bake and let cool.
Frost with your frosting of choice. I had a can of Rainbow Chip laying around and I was feeling lazy. Kids don't really care if it is real buttercream. They don't judge.