The procedures will take place within a portable play area, which includes toys and a partial body weight mobile harness system to assist the child in moving and exploring safely within the play area. Infants will always play and explore in this same area during the study but sometimes they will wear the PBWS harness and sometimes they will not wear the harness. During the intervention play sessions, the child will have the harness on. During the control play sessions, the child will play in the play area without the harness on. The child will participate in the intervention play sessions (using the harness) for 3 weeks, and in the control play sessions for 3 weeks. Before the first visit, this will be done randomly which group (intervention or control) the child will start with. Children will switch groups after week 5 of the study.~Week 1: assessment week, single session for 1 hour. At this first session, the investigators will do a developmental test for the child to see how they move around. This test will be videotaped. The investigators will also ask the caregiver to fill out a survey that asks caregivers questions about the motivation of their child and how they learn and play.~Week 2-4: play sessions, three times/week for one hour each. At each play session, the investigators will videotape the child playing and also place a small activity monitor on one wrist and one ankle. The session will end when the child has played in the play area for 30 minutes or the child has been present for 60 minutes, whichever comes first.~Week 5: assessment week, single session for 1 hour. The tests and surveys from the first week will be repeated. The child will then switch groups to or from the intervention group or the control group.~Weeks 6-8: play sessions, 3 times/week for one hour each. The child will participate in the same activities as described above but in the opposite group.~Week 9: assessment single session for 1 hour. The tests and surveys from week 1 and week 5 will be repeated a final time. The study will be over after this visit.~During all play and testing sessions, children will be given breaks as needed or if the caregiver request one. Caregivers will be able to play and interact with the child as they usually do throughout the play session and will be present in the play area with their children at all times.
To explore the effects of Partial Body Weight Support (PBWS) within an enriched play environment for infants with Down Syndrome (DS), who are not yet walking, to better understand how PWBS may impact their mobility; exploration; and overall activity level.~Hypothesis1 A: Infants will demonstrate increased movement counts on an ActiGraph during intervention compared to a control phase. Hypothesis 1B: Infants will demonstrate a higher frequency of exploratory behaviors during the intervention as compared to a control phase.~Hypothesis 2: Infants will demonstrate an increased rate of improvement in Gross Motor Function Measure scores after the intervention compared to a control phase.~Hypothesis 3: Infants will demonstrate higher parent-reported mastery motivation on the Dimensions of Mastery Questionnaire after the intervention compared to a control phase.