Blac Chyna: I've Got Womb for the Next Kardashian -

That didn't take long -- Rob Kardashian and Blac Chyna's kid is already in the family biz ... making his/her social media debut.

Chyna posted her sonogram with a long message about her little nugget, fairy tales, bundles of joy and blah, blah -- she's really happy about what's cooking in the oven.

Remember this pic. In a couple years this blob is going to be in a stroller pushed by big cousin North as they shoot a reality TV show. Look closely, you can see a tiny contract from Kris Jenner.

Meanwhile, the joy of parenthood was written all over mom and dad-to-be's faces during their Monday date night at the movies.