Intervention: Sitting Together And Reaching To Play (START-Play) is an intervention for infants with motor dysfunction or delay in which physical therapists visit the child's home to target work on siting, reaching, and problem solving. The therapist visits the home twice weekly for 3 months. During these visits, therapists and families work together to provide intensive, individualized, daily activities to advance reaching and sitting through small increments of challenge and support for these skills, which then become the building blocks for motor-based problem solving. More specifically, the intervention focuses on self-initiated, goal-directed movements to build orientation and attention to objects, while learning basic relationships of cause and effect. Infants and families in the intervention group will receive this intervention in addition to their usual early intervention services.