A pair of sisters have gone viral after their mom shared a video of the older sibling helping her younger sister, who has Down syndrome, with a dance routine. Nine-year-old Gracie and three-year-old Riley had the audience in tears, their mom, Jennifer McCormick, from Boston, Massachusetts, said. Riley has overcome a number of obstacles in her life, having been born with Down syndrome and congenital heart disease. The three-year-old has undergone two open heart surgeries and had a pacemaker fitted, and her older sister has been there to support her every step of the way. Riley has always looked up to Gracie, Jennifer said, and so when she saw her older sister dancing, she wanted to take part, too. At their local dance class, Gracie has been assigned as Riley's helper, and assists with practice when the pair are at home. The viral moment, which took place on April 26, happened at the girls' performing arts academy in Salem, Massachusetts, where they were undertaking a dress rehearsal.