Appearing on either side of their mother, the siblings, 11, danced inside large opened green presents before stepping out to help close out the number, after which a Santa performer was brought out on a float down 34th Street for the grand finale.
Moroccan wore a red sweatshirt, black pants and a gold chain, while Monroe was dressed up as a fairy in a white tutu, tiara and wings. The twins' outfits corresponded with those worn by adult members of the backup dance ensemble.
"Happy Thanksgiving!!!" Mariah, who was clad in a red mermaid gown and tiara for the performance, wrote on Instagram. "Grateful and so proud of my beautiful kids Roc and Roe, grateful for the lambily and for the precious moments in life."
The pop star, often dubbed the "Queen of Christmas," added, "Now it's reaaaallly time!!!"