Childhood obesity is becoming one of the most serious public health problems both in health and economic terms. This paper introduces a technological solution, “OB CITY” that supports the management of childhood obesity. The system mainly uses the behavior treatment, providing two types of user terminal for the parents and the children, through an establishment of a children's social network game, letting parents grow children with a scientific way, and letting children have good living habits and learn the relevant knowledge in the game, and get a normal value of BMI. The system is in a definition phase, and will be validated with user interaction experts, leading to a first mockup to be tested with end-users.