The study protocol for the randomized controlled trial conducted within STOP, the More and Less Europe study has now been published. The intervention will be conducted in three countries: Sweden, Romania and Spain. Three hundred children, 2-to 6-years old with overweight or obesity, will be recruited and randomized to one of two groups: 1) a parent support program focusing on parenting practices followed by a mobile based intervention to boost the effect of the parent program or 2) to standard care. The primary outcome of More and Less Europe is change in body mass index (BMI) z-score after 9-months and secondary outcomes include: waist circumference, eating behavior, parental feeding practices, objectively measured child physical activity, dietary patterns (based metabolic markers from urine), epigenetic and gut hormones, and the overall acceptance of the overweight and obesity management in young children through semi-structured interviews. Outcomes are measured at baseline and after: 10-weeks, 9-months, 15- and 21-months post-baseline. If the parent program is found to be successful, it has the potential to improve routine care of overweight and obesity in young children and the mobile application could prove to be a feasible option for families to up hold the effects of the care provided.