Thinking Like A Child

Has a child ever asked you why the sky is blue? You could give the adult answer:

The sun's light is really white to our eyes, but the subtractive effect from the preferential scattering of shorter wavelength light removes enough violet and blue light to leave a range of frequencies that is perceived by the human eye as yellow. It is this scattering of light at the blue end of the spectrum that gives the surrounding sky its color.

Or, you could just give the 100% truthful, child-worthy answer:

Q: Why is the sky blue?
A: Because there's a lot of blue stuff up there!