Aim 2: to monitor stress levels and safety risks related to use of constraint in the 3 conditions identified above (Aim 1). The study addresses stress levels in both the children and their parents, because CIMT is a high-intensity and unusual (i.e., constraining the child's "stronger arm") form of therapy taking place in the children's homes. Prior published clinical case reports indicate infants and toddlers adjust well to this form of therapy, and parents have favorable responses, no study previously has directly measured stress effects, related to self-report of parents or biological indicators, such as revealed by collecting saliva and hair samples to analyze for cortisol levels and changes over time.