I was wondering what others say for this too.

This topic came up recently with my 4yo (after watching an episode of Neighbours and one of the characters gave birth) - First she asked: How do babies get into your tummy? And I said Umm, God puts them there. Then the next question was: Where is it coming out? (As the midwife handed the baby to the mother) to which I replied: Near where you go to the toilet and she replied: Your bum! That's funny and then ran off laughing.