Show and tell

The following is my conversation with Mummy after a big feast last night.

Mummy: Bean Bean, you ate so much tonight, you must be full right?

Me: (Pulling up my top) Tummy!

Mummy: Yes that's right Bean Bean, your tummy is big because you ate a lot of food tonight.

Me: (Pointing at my tummy) Baby!!

Mummy: (Laughing) No Bean Bean! Big tummy doesn't mean you have a baby inside! Hahahaaaa

I thought I said the right thing because Auntie Elena's tummy is big and Mummy told me there is a baby inside... I don't get it now.