The work aims to take children as the research object to explore the interactive interface design method of smart watches that can generate the flow experience. Based on the flow theory in cognitive psychology, user evaluations were obtained through ROST CM6 text analysis word frequency software. Combined with children's psychological and behavioral characteristics, the interactive touch points in the process of using smart watches were analyzed. In addition, the three links of flow theory were decomposed into specific design points, and the design method of children's smart watches was constructed. Finally, the interactive design strategies and guiding ideas were proposed such as providing children with clear goals and tasks, vivid and interesting interface performance, efficient operation interaction, and immersive emotional experience. The validity of the flow framework and the rationality of design strategies were verified by design practice. The interactive interface design of children's smart watches based on the perspective of flow theory is helpful to improve the interaction efficiency of products, and has certain guiding significance for the combination of children's smart watches and flow theory.