RESUMEN
BACKGROUND: There is high interest in a new approach to improve children's lifestyle habits in order to prevent childhood obesity. A smartphone application (app) is a new technology platform that can be used to prevent childhood obesity. METHODS: The key messages for healthy eating habits and physical activities were selected by experts in nutrition, physical activity, and psychology and were adjusted for use in elementary school students. Gamification techniques were used to increase app user engagement. A total of 249 students in grades 4-6 were asked to rate their satisfaction for the app after 4 weeks of use. RESULTS: The main menu of "HAPPY ME" was composed of user profile, "EVERYDAY QUEST," exercise diary, diet diary, settings, and notifications. The app users were asked to complete 6-9 daily missions regarding healthy eating habits and physical activities through "EVERYDAY QUEST." The mean satisfaction scores for each variable were distributed from 3.6 to 4.0 points, and most of the students responded that they would continue to use the app (4.0 points). CONCLUSION: We developed a smartphone app (HAPPY ME) for 4th-6th grade elementary students aimed to provide educational information about healthy eating habits and physical activities in order to prevent childhood.