The objective was to establish how stakeholders in low- and middle-income countries (LMIC) conceptualize child mental health impact. Semi-structured interviews were conducted with 18 stakeholders from disadvantaged urban communities in Kenya, South Africa, Turkey and Brazil. Participants represented education, welfare and health care agencies; as well as community and religious groups. Data were analysed through a thematic approach and three related themes were identified. Impact was defined as a process of change, with child-centred outcomes and measures that were broader than mental health symptoms improvement. Beneficiaries were identified at child, family, community and service level. Participants wished to see strategies that ensured sustainability of impact, namely child mental health policy, stakeholder engagement, interdisciplinary working, and capacity-building for all stakeholder groups. Child mental health service transformation in LMIC, especially in areas of deprivation, needs to build on existing resources and strengths by co-producing psychosocial outcomes with a range of professional and community stakeholders. Impact on children's mental wellbeing can be achieved through a co-ordinated strategy that involves designated policy, capacity-building, and interdisciplinary networks with meaningful community involvement.