Technology and digital media (TDM), which includes TV viewing, playing computer games, and mobile device use, is common among preschool aged children. Many young children exceed the recommended <1 hour/day of parent supervised TDM use. This is concerning because excessive TDM use has been linked to health problems, such as higher risk of overweight and obesity among children. The pathways linking TDM use with risk of obesity have not been robustly established, but sleep is one hypothesized mediator that warrants investigation. Any impact TDM has on child sleep could also influence other health and developmental outcomes previously associated with poor sleep in children. Past studies of TDM use among young children primarily relied on parent report of children’s typical use of TDM, resulting in both over- and under-reporting of TDM use. The validity of findings from these past studies are therefore questioned. FLASH-TV is a new technology developed by our team to passively, objectively measure children’s viewing of large digital screens, such as TVs or video- game consoles. In this proposal we propose to leverage FLASH-TV along with new approaches for measuring children’s use of mobile devices, to robustly assess children’s use of TDM across multiple platforms (TV, mobile devices, and videogame consoles) over 10 days at two time-points, 12 months apart. We will combine the novel TDM use assessment with robust, valid approaches for measuring children’s sleep (wrist-worn acigraphy) in a diverse cohort of 4-year old children (n=200). Height and weight will be collected on the children and parents. Parents will report on home environmental variables that are hypothesized to influence the child’s TDM use (TDM parenting practices, TDM inventory of the home, parents’ outcome expectations for child’s TDM use, and neighborhood disorder) and sleep (sleep parenting practices, child’s sleep hygiene environment, parents’ outcome expectations for child’s sleep). For the first time, these novel approaches to passively and objectively measure children’s TDM use in their home environment over multiple days allows us to assess the with-in and between child association of children’s TDM use and children’s sleep at baseline and over 12 mo. This study design will also allow us to more robustly assess the association between children’s TDM use and their weight status over 12 mo, and whether sleep mediates the association between TDM and weight status. Lastly, we will explore the association of the home and social environments on children’s TDM use and sleep in cross-sectional and longitudinal models. To promote synergy and cost-effectiveness within this program grant, the cohort established in project 1 will be leveraged by project 2 to investigate the impact of TDM use on children’s developmental outcomes. A Digital Assessment Core will provide the technology and processing support for the TDM and sleep assessments of all projects and a Biostatistics and Database Management Core will ensure harmonization of variables, database integrity, and statistical support. This project will thereby help provide the first robust data for the influence of TDM use on children’s sleep and weight status to inform future guidelines.