My mother was giving my newborn sister a bath. My brother (age 3 at the time) and I (age 7) were watching the event.
My brother and I both noticed the anatomical discrepancy.
My brother said, "Mommy, where's her wee-wee?"
And in my role of the big brother, I said, "Stupid. She's just a baby. She'll grow one."
My mother laughed so hard she almost dropped the baby.