Childhood overweight and obesity are significant risk factors for elevated cholesterol, blood pressure, and cardiovascular disease throughout the life course. Although parents exert one of the strongest influences on children’s health, parent‐focused programs to prevent and treat child obesity have had modest success. Parental stress is an understudied factor that may compromise parenting practices related to children’s dietary intake and physical activity. However, research linking parental stress and children’s obesity risks has suffered from weaknesses including cross‐sectional designs, retrospective measures of stress, the failure to consider within‐day processes, and a lack of focus on mediating mechanisms—leaving little information to guide the development of prevention and treatment programs that reduce the effects of parental stress on children’s obesity risk. To address this gap, we propose a longitudinal study testing a novel conceptual model purporting that the effects of parental stress on children’s physical activity and eating behaviors operate through within‐day processes that contribute to children’s long‐term obesity risk in an accumulated manner over me. In the proposed study, 200 working mothers and their 9 to 11 year‐old children will participate in 6 semi‐annual assessment waves across 3 years. Ecological momentary assessment (EMA) and salivary cortisol sampling methods will capture within‐day processes—which have been concealed in prior work. Each assessment wave will consist of EMA, salivary cortisol sampling, accelerometer monitoring, and 24‐hour food intake recalls across 7 days in combination with retrospective paper‐and‐pencil surveys; and height, weight, and waist circumference assessments in mother and children. This project is the first of its kind to use an innovative, real‐time data capture methodology to examine the within‐day and long‐term effects of maternal stress on children’s eating,physical activity, and obesity risk. The results will inform the development of novel interventions that help working mothers to reduce the negative effects of stress on weight‐ related parenting practices and foster family environments that can buffer the effects of maternal stress on children’s obesity risk. Given the detrimental health effects of childhood obesity, such information could be of significant value to efforts to improve public health.