Rumer Willis is the best big sister ever ... her much younger sibling Mabel — and the pair got together to sing an original song for her Instagram followers. MORE: Gwyneth Paltrow's Kids ...

communication," in a sing-song voice. Never miss a story — sign ... news to compelling human interest stories. Courtesy of Rumer Willis "It's so silly, but it's all about taking your baby's ...

Rumer Willis is celebrating a new mom milestone ... Willis then proceeded to sing the song. Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best ...

Rumer Willis, 35, loves to see her parents ... Rockettes' Radio City Christmas Spectacular," but now she mostly sings songs from "Annie" to her two daughters … while they beg her to play ...

Rumer Willis, Scout Willis and Tallulah Willis. Moore shared a video on Instagram that shows Willis joining in as the family sings "Happy Birthday." "Happy birthday, BW! So glad we could celebrate ...