<p>Part of the appeal of digital health interventions, including mHealth, is the potential for greater reach in places where conventional health promotion is hampered by geographical, financial or social barriers. Yet, 'engagement' – typically understood as user experience and interactions with technology - remains a persistent challenge, particularly in places where technology access or familiarity with technology is limited. We undertook an evaluation of a childrearing app to promote socioemotional and cognitive development in early childhood across the world. In this article, we present findings from qualitative research on app rollout in Indonesia, the first of numerous low- and middle-income countries targeted by the app. We draw on systems theory and complexity thinking to broaden the lens of 'engagement' beyond individual users to encompass collective systems (families and communities), exploring how the intervention was harnessed to meet local contextual needs. The qualitative research involved semi-structured interviews, workshops and audio diaries with 57 diverse stakeholders, including Indonesian parents, caregivers, and collaborators involved in funding, development, and dissemination of the app. We observed the importance of social connection, sense-making, and interactive learning for enhancing engagement with the app and its messages. Enthusiastic users, strongly linked across community networks (e.g. kindergarten teachers), improvised dissemination strategies to facilitate uptake. Interactive learning that tapped into familiar social structures (e.g. intergenerational hierarchies) was crucial for engagement. Understanding ways the app failed to tap into structures of social connection served to highlight the need to embed strategies to support collective engagement.</p>