Early childhood is a critical period of life when nutritional choice and mealtime routines develop and obesogenic tendencies may be established. There is a need for greater understanding of toddlers and how parent-child interactions over time and across contexts relate to development of obesity. The purpose of this protocol paper is to describe the recruitment strategy, protocol, and characteristics of participants in the Play and Grow cohort. Between December 2017 and May 2019, three-hundred caregivers and their 16- to 19-month-old toddler (57 percent male) were recruited from records of the major pediatric provider in Central Ohio and enrolled in an ongoing 2-year prospective study. The cohort is diverse in race and ethnicity, parent education and age, household income, and family composition. Thirty-seven percent of children were born preterm (less than 37 weeks gestation). The first visit, completed by 299 families at mean (SD)18.2 (0.7) months child calendar age, included video-recorded parent-child interaction during play, anthropometric measurements, and caregiver questionnaire. Six months later, a home visit completed by 284 families included observation and video-recording of parent-child interaction in mealtime and non-mealtime contexts. This diverse cohort is being followed prospectively through ongoing home and laboratory visits at child ages 36 and 42 months. Growth trajectories of children will be analyzed in relation to self-regulation and quality of parent-child interaction.