The following conversation occurred between me and my daughter in the car on the way to catch the bus after dropping my son off at pre-school.
Daughter: Dad, how do babies get out of their mommies' tummies?
Me: [pausing to consider - Truth? or Lie? WTF!] Um, usually they come out of their vaginas.
Daughter: What the heck!?!?!?!
Me: Uh, yeah, sometimes a doctor has to take them out of the tummy, but ususally they come out of the vagina.
Daughter: [dumbfounded]... But, vaginas are so small...
Me: Well, babies are pretty small, too.
Daughter: NOT AS SMALL AS VAGINAS!
Me: [really hoping this conversation is over soon] Yeah, well, you're right. I guess vaginas get bigger when you have a baby.
With that, I was relieved that Emma had no further questions. She quietly pondered the implications of this. I would have loved to know what she was thinking, but was not at all prepared to go into further detail about it. I later called her Mom to let her know she should expect questions along these lines.
I guess the notable thing to take away from this is that, in addition to her increasing understanding of biology, it's pretty clear Emma also has a good understanding of spatial relations. So, that's good.