Out of the mouths of babes...
As Superman Returns, now in heavy rotation, came on recently the following conversation transpired:
Scriblerus Fille: Daddy who's that?
Mr. Scriblerus: That's Superman.
Scriblerus Fille: Why does he fly?
Mr. Scriblerus: You see, Superman was born on the planet Krypton, when that planet was destroyed he was sent to earth by his father Jor-El in a spaceship. The spaceship landed in Kansas and Superman was raised as Clark Kent by his adoptive parents. Because the planet Krypton has a red sun, and Earth has a yellow sun, Superman has super powers like flying...
Scriblerus Fille: Daddy, that's silly.
n.b. Scriblerus Fille is 4 years old.