The Birds and Bees by Dr. Greta

To be honest,  with three brothers, I should've expected this conversation to come sooner than later but today was the day that Isabel asked the question while I'm changing Zeke's diaper.  It went a little something like this:

Isabel: "why does Zeke look like that?"
Mommy: "that is Zeke's boy part."
Isabel: "yes, I know that but why does it look like that."
Mommy: "Because boys and girls have different parts."
Isabel: "yes, I know that but why does his look like that!"
Mommy: "you know how you have an outy belly button and Mommy has an inny belly button?  Well, girls have inny pee-pee parts
                  and boys have outy pee-pee parts.  It's the way God made us."
Isabel: "oh, okay!"