This article explores children’s collective participation in universal preventive initiatives aimed at promoting supportive social environments and favourable conditions for children’s upbringing. In several municipalities and regions, such initiatives are being developed inspired by the “Scottish model,” a child rights–based framework for social services, preschool, school, health care and the police, focusing on coordinated early interventions. These ambitions align with the new Social Services Act’s emphasis on knowledge-based collaboration and preventive work for children in accordance with human rights. Within the field of children’s rights, participation is central and includes involvement in collective matters affecting groups of children, such as uni­versal preventive initiatives. Professionals’ understanding and agency are crucial for children’s collective participation. Pre­vious research, however, points to uncertainty among professionals regarding how to work with participation in this context. Drawing on critical children’s rights perspectives and two research activities conducted in close collaboration and dialogue with professionals, this article examines children’s collective participation at the intersection of practice, research and child rights ambi­tions. It contributes knowledge about how professionals understand opportunities and obstacles related to collective participation in universal preventive initiatives. The analysis shows that professionals understood collective participation differently depending on whether they relied on established practices or scientific definitions. When remaining within existing structures, participation was primarily framed as indirect involvement, whereas enga­ging with scientific definitions opened up space for more direct forms that challenge established practices. In the discussion, these approaches are interpreted as positioning children either as knowledge holders or knowledge actors, raising questions of power and scope for action. Ove­rall, collective participation emerges as a complex terrain shaped by uncertainty, high demands and inherent tensions, where strengthened knowledge, organisational support and a clarified purpose are essential to reinforcing children’s position in universal preventive initiatives.