Kylie Jenner knows how to make her man happy! Her man, King Cairo, that is ...

The youngest of the Kardashian-Jenner clan -- only 19 -- is playing mom to boyfriend Tyga's and soon-to-be-sister-in-law Blac Chyna's son King Cairo. She's certainly young to play the role of step-mom, but she seems to enjoy it.

Kylie took the tyke to stock up on toys ... she knows the way to his heart!