Glasses, water, food coloring
Teach your child how to mix two colors together to make another color (e.g. yellow+blue makes green and red+blue makes purple). To begin, fill up a couple of clear glasses with water. Then, allow your kids to add drops of food coloring to make your color mixes -- you can use this part to teach older kids basic addition. The kids will have fun experimenting -- make a yellower green by adding more yellow than green, make a redder purple by adding more red than blue, dump all of the glasses together to make brown!