Where do babies come from?

So Noah kept asking this, over and over and over again.  I remembered a line from a movie (probably a horrible one) where they said something to the effect of "mommy and daddy wanted a baby so much that they closed their eyes really hard and made a wish."  Since under 4 seems a bit early for The Talk, I opted for this PG version.  That led to this conversation today:

Noah: I have 3 robot babies in my tummy
Ava: Real or pretend?
Noah:  Real.  Because I closed my eyes really hard
Ava: And made a wish!  How are the robots coming out of your tummy?
Noah: Well, the Dr will cut a hole in my tummy and take them out.

Side note, I got tired of my kids referring to c-sections as the only way to get babies out of tummies so one day I told them where they are supposed to come out of.  Ava's response: Mommy you're silly!  That's gross!  That's where pee comes from, not babies!

I am at a complete and total loss.  I thought we had a lot longer before we had to deal with these things!