Mommy: "Um... what do you mean?"
Rebekah: "Mac's bum is different." (Mac is Daddy's 3-year-old cousin. He is Rebekah's friend.)
Mommy: "Because boys and girls are different."
Rebekah: "Why?"
Mommy: "Because Heavenly Father made us that way."
Rebekah: "Why?"
Mommy: [[mumblemumblemumble]]
Of course, since we don't have any boys yet, so far all of this sort of education rests solely on Andrea's shoulders.
Andrea loves these semi-related images in blog posts SO much I just had to find a good one for her.