The aim of this study was to examine the implementation of an interdisciplinary collaboration between health nurses and kindergarten pedagogues within a health promotion intervention designed to reduce health inequality among children. The collaboration took place during group- and play-based assessments of motor development in 4-year-olds. A total of 12 participant observations and 10 interviews (5 with health nurses and 5 with pedagogues), were used to explore the collaborative challenges and strengths. Through abductive analysis we examined four analytical themes: 1. The various roles assumed by the professions, 2. Their differences in motivation, 3. The professions' attitude toward each other and the collaboration, and 4. Diverse expectations regarding responsibility and follow up. These themes collectively offer insights into interdisciplinary collaboration in the context of health promotion and play-based assessments. The findings reveal differences in professional status and roles, with the health nurses assuming authoritative positions while the pedagogues adopt more assisting roles. Ambiguity regarding follow-up responsibilities furthermore emerges, potentially undermining the professionalism, empowerment and agency of the pedagogues. The study suggests future interventions to consider equity and professional recognition to enhance collaboration quality and implementation effectiveness.