Objective: This study explored how professionals in interdisciplinary teams perceived the implementation of the World Health Organization's International Classification of Functioning, Disability and Health, version for Children and Youth (ICF-CY) in Swedish habilitation services. Design: Descriptive longitudinal mixed-methods design. Methods: Following participation in a 2-day in-service training on the ICF-CY, 113 professionals from 14 interdisciplinary teams described their perceptions of the implementation of the ICF-CY at 3 consecutive time-points: during in-service training, after 1 year, and after 2.5 years. Results: Implementation of the ICF-CY in daily work focused on assessment and habilitation planning and required adaptations of routines and materials. The ICF-CY was perceived as useful in supporting analyses and in communication about children's needs. Professionals also perceived it as contributing to new perspectives on problems and a sharpened focus on participation. Conclusion: Professionals indicated that the ICF-CY enhanced their awareness of families' views of child participation, which corresponded to organizational goals for habilitation services. An implementation finding was a lack of tools fitting the comprehensive ICF-CY perspective. The study points to the need for ICF-CY-based assessment and intervention methods focusing on child participation.