Abstract Background Nearly 60,000 people applied for asylum in the Netherland in 2015, confronting the governmental structures and services with great administrative, logistical and service provision challenges. Refugee children’s psychosocial needs and wellbeing are often overlooked, and post-migration support is of pivotal importance. Methods An easy accessible movement–based psychosocial intervention, called TeamUp, was developed for children aged 6–17 living in refugee reception centres. A mixed-method process evaluation was conducted of (1) implementation process, assessing attendance (n = 2183 children, and n = 209 children); (2) implementation quality, using structured observations at two time points to evaluate facilitator’s (2a) individual-level fidelity (n = 81 facilitators); (2b) team-level fidelity (n = 22 teams); (2c) facilitators’ competencies (n = 81); (2d) trainee perceived self-efficacy pre-post training (n = 73); and (3) perceptions on implementation and outcomes, employing a survey (n = ...