Unlabelled: Obesity in children and adolescents is rising in China and globally, with health consequences that are already evident during childhood. This Viewpoint represents the authors' interpretation of current evidence and policy experience, using China as an illustrative case for a wider international challenge. We argue that social media should be considered a modifiable obesogenic environment because it can amplify sedentary behavior, digital food marketing, disrupted sleep, body image pressures, cyberbullying-related distress, and reward-based design that encourages prolonged device use. The aim of this Viewpoint is to explain why proportionate regulation of social media should be included in childhood obesity prevention. We make 4 key arguments: digital food marketing and persuasive platform design require stronger age-sensitive governance; regulatory approaches should be differentiated by developmental stage and social context; AI-assisted moderation may support enforcement but requires safeguards; and regulation should complement, not replace, school-based education, family engagement, and healthy technology design. The intended audience includes public health researchers, clinicians, policymakers, platform regulators, educators, and child-health advocates in China and internationally.