Eight-year-old son (watching the rabbits in our yard):  How do you tell the boy bunnies and the girl bunnies apart?
Mom:  From here, we can't.  You'd have to get really close to tell.
Eight-year-old son:  So if we got close, how would we tell?
Mom:...uh...pick them up and check them for parts, I guess.
Eight-year-old son:  What parts?
Mom:  Honey, you're smart enough to know the difference between boys and girls.  What parts do you think?
Eight-year-old son:...Oh, like long hair!

(yes.  Exactly like long hair.)