The guest of honor arrived to her event in full princess regalia ... she rode in a horse-drawn carriage with mom and dad, while wearing a bright pink dress and, of course, a tiara.

Cardi's outfit matched her little girl's and they made a grand entrance together -- through a tunnel of balloons -- into the castle. The party had the usual kid stuff ... a petting zoo, Disney princesses and a Cinderella cake, but also a DJ to make sure Cardi and Offset had fun.

While the happy couple was grinding on the dance floor ... Cardi's baby bump was very prominent.

Cardi just revealed -- during her BET Awards performance with Migos -- she's expecting their second kid.