Weight status differences are present upon entry into kindergarten, indicating that the origins of overweight/obesity (OWOB) develop before elementary school. Preschoolers (3-4-yr-olds) may also experience accelerated weight gain (i.e., increased zBMI) during the summer and lose weight (i.e., decreased zBMI) during the school year – indicating that summer may play a key role in developing OWOB. Preschoolers from low-income households (i.e., 185% or less of poverty level or Medicaid eligible) are at the greatest risk for accelerated summer weight gain. In general, we don’t know the places preschoolers go, who they are with, and what they do during the summer that may influence their health behaviors and weight status. In the US, many center-based childcares operate on an academic/school calendar (Aug-May), and 60-80% of preschoolers attend center-based care. Preschoolers who attend formal center-based childcare are less likely to develop OWOB by 1st grade compared to preschoolers who receive home-based care. We believe attending center- based childcare lowers the risk of OWOB through daily rules/routines that promote healthy behaviors (e.g., PE/recess, healthy meals, consistent sleep schedules at home). Center-based care facilitates the acquisition of motor skills and fosters executive functioning/self-regulation – key factors in the development of OWOB. During summer, fewer than 30% of preschoolers attend center-based childcare. For many preschoolers, especially those from lower-income households, summer may be an extended period away from formal center- based childcare that promotes unhealthy behaviors, loss of motor skills, and loss of executive functioning, which could lead to excessive weight gain. We will conduct an observational cohort, enrolling 3-4-yr-old children attending needs-based (185% or less of poverty level or Medicaid eligible) center-based childcare during the academic/school year and follow them for 2 years (2 school years and 2 summers) as they transition from preschool into elementary school. Measures of anthropometrics, motor skills, and executive function will be collected before school ends and upon return from summer vacation. Health behaviors (i.e., activity, screentime, diet, and sleep) will be collected during April/May (school) and July (summer) along with information about social- and setting-specific influences. The following aims will be addressed: Compare longitudinal changes in anthropometrics (primary outcome), health behaviors (secondary outcomes), and motor skills and executive function (tertiary outcomes) during school and summer; Identify individual, family/home, neighborhood, and school/community influences that moderate changes in anthropometrics, health behaviors, motor skills, and executive function during school and summer; and Qualitatively interview parents about their child’s school and summer experiences and health behaviors.

Preschoolers (3-4-yr-olds) experience accelerated weight gain (ie, increased zBMI) during the summer and lose weight (ie, decreased zBMI) during the school year. We don’t know the places preschoolers go, who they are with, and what they do during the summer that influences their health behaviors and weight status. This project will open new opportunities in obesity prevention by establishing the need to focus on preventing excessive summer weight gain among preschoolers.