Children's healthy active living (HAL)-encompassing nutrition, physical activity, and sleep-is shaped by complex socio-ecological factors spanning individual, familial, environmental, and societal levels. For newcomer families, migration introduces additional challenges that can deprioritize health-promoting behaviors amid competing settlement demands. This article presents insights for researchers and practitioners from the Strengthening Community Roots: Anchoring Newcomers in Wellness and Sustainability (SCORE!) research program, which co-designed a child-focused HAL intervention with immigrant families in Hamilton, Ontario, Canada. Grounded in a socio-ecological framework, SCORE! employed a participatory, community-engaged approach to address structural inequities and foster culturally responsive health promotion. The tripartite methodology included: (A) synthesis of evidence on nature-based HAL interventions; (B) multi-level community engagement through trust-building, photovoice, co-design workshops, surveys, environmental mapping, and policy dialogues; and (C) implementation and evaluation of co-designed interventions aimed at enhancing children's self-efficacy for physical activity. By positioning families as co-creators rather than passive recipients, the project mobilized local knowledge and fostered community ownership. This work contributes to the growing field of knowledge mobilization in health promotion research and offers practical lessons for designing sustainable, community-driven HAL initiatives in diverse urban settings.