Why the sky is blue
How to explain diffuse sky radiation to a kindergarten student:
Like the ripples in a pond, light is made of waves. Red light is long waves. (Make a gesture.) And blue light is short waves. (Make a gesture with more tightly spaced wiggles.) You remember the rainbow, right? The farther down the rainbow, the longer the waves. Now the sky lets the long red and yellow waves go straight from the sun to the ground, but the shorter blue and violet waves bounce around in all different directions. So when you look at the sky, you see the blue light that bounced off that part of the sky. Sunsets are red because sunlight has to go through so much sky that most of the violet, blue, and even green are scattered out before it gets to your eyes.
Once you get done with school, you'll figure out why the short waves bounce.