Where do babies come from?

The other night Cameron and I were laying in our bed and he was reading me his stories and he asked me "mommy how does God put a baby in your belly?" Needless to say I was shocked with this question since it just came out of the blue. I really wasn't sure how to answer the question, a little unprepared. So I told him that when a mommy and daddy love each other very much they become very close and he said "like hug" and I said yes. Then he proceeded to ask me if I had a baby in my belly and I said no and asked him why he thought I had a baby in my belly, and he responded because you and daddy hug a lot.
I can't believe he is that age where the questions are going to start coming, I guess I better start figuring how I am going to answer these questions on life. The fun has begun...