Childhood overweight and obesity is an increasing health problem globally, and can be established as early as 2-5 years of age. Mobile phone based (mHealth) interventions have been successful for weight management in adults; however, their potential in young children is yet to be established. Therefore, the ultimate goal of MINISTOP (Mobile-based INtervention Intended to STop Obesity in Preschoolers) trial is to help parents of four year old children to achieve a healthy weight and body fat via a smartphone app (MINISTOP). More specifically this trial aims to reduce body fat (primary outcome), increase the intake of fruits, vegetables as well as decrease the intake of candy, and sweetened beverages, and increase the amount of time spent in moderate-to-vigorous physical activity and decrease sedentary behaviors (secondary outcomes) in healthy preschool aged Swedish children. If the MINISTOP app is effective, it has the potential to be incorporated into the child health care to aid in counteracting overweight and obesity.