"With the beautiful @serenawilliams backstage tonight," Carey captioned a pic of herself and her kids posing with Williams.
Carey opened for Lionel Richie at the concert, and Williams -- who went to the show with her mother, Oracene Price -- was sure to Snapchat her love for their performances. The mom-to-be thoroughly enjoyed seeing the 47-year-old diva crooning "We Belong Together," and had an all-out singalong when Richie hit the stage.
After the show, Carey and her adorable kids indulged in some sweets at the concert after-party at Miami Beach's Sugar Factory American Brasserie. Roc was all about that cotton candy, and we don't blame him!