Grady's Daughters refer to the two girls in blue Danny Torrance sees while riding in the Overlook Hotel's West Wing.

Speculation is that the girls are not twins. While they mirror each other, remember that anachronistically, a lot of families dressed their offspring in similar, matching fashions. Also, their dresses are designed to be different and one is up higher than the other. One also appears to be slightly taller. While Stanley Kubrick may have cast a real set of twins (Lisa and Louise Burns) in the role, note that they have been intentionally made to look differently.