How did Mary gave birth to Jesus?

So it started, the how-did-the-baby-got-out-of-the-tummy question.  Beata is learning more about the birth of Jesus in her Sunday classes, and while we were driving home from dropping off Jakob from school, she bursted out this question with a phrase, "there was no door, how did baby Jesus got out?".  I was speechless but then I quipped, only God can do miracles.  She's smart, but I'm smarter :)