Empowering children and adolescents to adopt healthy lifestyles while tackling health inequalities is crucial. Person-centred interventions have been developed to this end but face several challenges: they are often restricted to one specific actor of children’s environment (teachers, parents, or peers) and rarely target several significant others simultaneously, they are often restricted to one specific behaviour (e.g., physical activity) or life domain (e.g., school), their effectiveness may differ according to socio-economic or socio-spatial conditions, and they are rarely both large-scale and personalised to individuals' needs. To address these challenges, and in line with the call, the ambition of YEAH! is to develop an innovative personalised person-centred digital intervention that: (1) promotes children (8-10 years) and adolescents’ (14-16 years) social interactions with multiple actors of their environment, (2) targets multiple health behaviours (physical activity, sedentary behaviours, diet, sleep), (3) combines in a novel manner evidence-based knowledge of optimal intervention features (theory-driven approach), with co-creation with end-users and stakeholders (data-driven approach) to tailor the intervention to the local context and target group, and (4) relies on a state-of-the-art method of intervention development to rigorously measure and verify its impact, optimise its sustainable implementation in the community and its equity, and evaluate its cost-effectiveness. To do so, YEAH!, which is coordinated by a woman researcher, will articulate interdisciplinary methods and concepts from psychology (health, social, developmental), public health, psychiatry, social marketing, geography, geomatics, environmental epidemiology, IT and computer sciences, statistics, physiology, and medicine, and on the participation of stakeholders (children and adolescents, parents, teachers, healthcare professionals, educators, local and national authorities).