This research study will examine young children with Down syndrome's initial experiences with mobility devices. Children's biomechanics and exploration will be quantified while they are using both an overground partial bodyweight support system and powered mobility device.

Young children with Down syndrome experience delays in cognition, communication, and mobility. As a result of cerebellar hypoplasia, children with Down syndrome have altered balance and coordination, muscle hypotonia, decreased muscle strength, and ligament laxity. Low muscle tone and ligament laxity can lead to the adoption of unfavorable postures, putting children at risk for developing musculoskeletal disorders in the future.

While children with Down syndrome are expected to walk, they do so significantly later than their peers, creating a gap in mobility, exploration, and socialization in the first years of life. Mobility during the first years is crucial to facilitate cascades of reciprocal development in cognition, communication, and motor skills, as well as reduce developmental delays and participation disparities for children with Down syndrome compared to their peers. While early intervention is common during this time to facilitate movement, clinical practice patterns vary widely and there are few evidence-based interventions or assistive technologies to support children and their families.

Treadmill training is currently the only intervention that has demonstrated efficacy for young children with hypotonia, but only for improving walking speed among already ambulatory children. Traditional treadmill training is limited, however, in that it does not allow for the sensorimotor experiences and social interactions that occur with self-initiated mobility in enriched, and often unpredictable, natural environments. As such, treadmill training and other clinical interventions may not fully address the need for holistic and multi-modal mobility opportunities.

Augmented mobility - in the form of partial bodyweight support systems, gait trainers, and powered mobility - has been proposed as a promising and complementary intervention to support early development in Down syndrome. While these tools have the potential to bridge the gap in self-initiated mobility and accelerate the onset of independent walking, little is scientifically known about how children engage with these devices nor how these devices shape their interactions with their environment. Furthermore, there is a lack of knowledge concerning the impact of different mobility devices on a child's physical development and posture.

In this research, the investigators propose to quantify a child's exploration, posture, and motor control strategies while using two promising assistive technologies for pre-ambulatory young children with Down syndrome: a partial-bodyweight support system (PUMA, Enliten, LLC.) and a powered mobility device (Explorer Mini, Permobil) that can be used in both seated and standing postures.

Participants will attend a total of four play sessions where they will play with a) no devices, b) partial bodyweight support, c) in the Explorer Mini in a standing posture, and d) in the Explorer Mini in a seated posture.

Inclusion Criteria:

• are able to sit upright independently
• are able to tolerate moving through space while upright for 30 minutes
• are under 35 pounds in weight
• are under 39 inches tall in height
• developmental delays and conditions that affect mobility and muscle tone

Exclusion Criteria:

- are able to walk 10 ft independently