The emergence of crawling and walking is significantly delayed in infants with Down syndrome (DS), but the development of independent mobility provides infants with new opportunities for exploring the environment and interacting with objects and people that are important foundations for early learning. Increasing infant mobility early in development with body weight supported harness systems may support infant exploration, communication, and social interaction. This project will set the stage for the first clinical trial of a mobility-related intervention specifically tailored for infants with DS by testing the feasibility of harness systems with infants and families and identifying measures that will serve as primary outcome variables. Upon completion of this pilot project, necessary preliminary data and experience required for an in-home, high-impact clinical trial for infants with DS will have been obtained.