Big questions: Where do babies come from?

In bed, last night, EggEgg suddenly asked, "Mami, when me and Cola and Daddy were all inside your tummy, were you very fat? 你係唔係好鼻(肥)?"

"Huh?" I was taken aback with this sort of question coming so soon.

Technically there are 2 errors in his statement. First of all, I am NOT fat!! Secondly,

"Erm, no. Daddy did not come from my tummy. Daddy came from Ah Mah's tummy, and I came from Poh Poh's tummy. I told you before, Ah Mah is Daddy's Mami, and Poh Poh is Mami's mami. Understand? (Trust me, this is actually fairly complicated to explain. I need a whiteboard and a power point presentation, please.)

"Then, Daddy and I used to live in different places. When we grow up, we got together and we made you." (Whew... I got it easy this time round. No further questions on how we made you.)

EggEgg nodded and ventured a conclusion, "So I came from Mami's tummy, and Cola came from Daddy's tummy?" (Hmm... this is kinda logical too, since there is substantial visual evidence based on the size of Tonton's beer belly.)

As much as I want to say, "Yeah, go ask Daddy when his baby will pop out", I had to act serious and explained, "No, no, both of you come from my tummy. Only girls can have babies. Boys can't have babies."

"係咩? 我唔知添! Oh really? I didn't know that." Then he shut his eye and said good night. Whew!