How does the baby get inside the belly?

How do you talk to a five year old about where babies come from? This question keeps coming up over and over again. Apparently my answers just lead to more questions. I try to be as honest as possible with Curtis within reason. At least he doesn't believe I ate him anymore. I once showed him a picture of me while I was pregnant and told him he was in my belly.
He said, "Did you eat me?"
"No."
"Well how did I get in there?"
"Jesus put you in there so you could grow and be born"
It took him a long time to believe that I didn't actually eat him.

So yesterday, on the drive to Tae Kwon Do, the conversation in the car was something like this:
Curtis: "Did Jesus tell you that my name was Curtis?"
Me: "No. Mommy and Daddy picked out your name." I went on to explain that Grandma Linda's last name used to be Curtis before she got married and that my mom's last name used to be Jackson before she got married. I also explained that my last name used to be different and when I married Daddy, I changed it to his last name so we could be a family. He asked curiously, "When I get married will I have a different last name?"
This led into "Do you get married first, then have a baby?" It all comes back to how babies come to be.

Now he knows all about the C-Section and how the doctor cut open my belly and got him out. "But how does the baby get in the belly?" UGH!!!

I tell you... I have researched and can not find an age appropriate book to answer this question for him. Any suggestions are welcome!