Confusing a Three Year Old...Where is my camera?

Y'know how you dread the question "where do babies come from?" I mean, how the heck to explain intimacy to someone that small?
Well, before that, there is the other question. "Mom, why is your tummy getting so big?"
For us, it hasn't been so much of a direct question, due to Esther's speech problems, than it has been a battle to keep them from squashing me. Any time I sit down, it's a race to Mommy's lap for tickles, which inevitably ends in my getting kicked, or squashed, or head-butted in my baby bulge. So Jeff and decided to tell Esther that she needs to be careful because there is a baby growing in Mommy's tummy.
I have never seen such a puzzled look on her face before. It was priceless!
First she looked at me, then my tummy. The baby isn't quite moving enough yet for her to see the bumps and movements yet, so after a long moment of confusion...she lifts up her own shirt and looks down at her tummy! She said something vaguely resembling "baby in tummy?", at which point we had to explain that only mommies have babies in their tummies.
I still don't think she gets it. Still, what I would have paid to have my camera on hand to capture that look!
I'm hoping as I get bigger, and the baby's movements become more pronounced, Esther might get the idea. We've told her she is getting another baby sister, but I don't think she quite gets it yet. Until the baby actually comes, and she has tangible evidence in front of her, she'll just think that Mommy is getting fat.
Thank goodness it doesn't matter to kids as much as adults!