Background <p>Children with special healthcare needs (CSHCN) live with long-term physical, developmental, behavioural, or mental conditions that affect everyday functioning and require specialized care. According to the International Classification of Functioning, Disability and Health (ICF), such conditions may cause impairments in body functions and structures, limitations in activities, and restrictions in participation, shaped by environmental factors. Evidence on social participation and its correlates in CSHCN remains limited. Therefore, we aimed to identify which correlates are associated with social participation across different conditions and indications in a multi-site sample of CSHCN in Social Paediatric Centres (SPCs) in Germany.</p> Methods <p>This study analysed parent-reported data of CSHCN (3–18 years) from the baseline of the PART-CHILD cohort collected in routine care in 15 SPCs in Germany (2019–2020). Social participation (outcome) in home, community, school, and living activity domains was assessed using the German Child and Adolescent Scale of Participation (CASP). In the regression analysis, independent variables included environmental factors (parental educational attainment, German native language) and health-related factors (impairment type and complexity reported as reason for referral to the SPCs, health-related quality of life (HRQoL)), as well as age (operationalised in groups [3–6; 7–10; 11–18 years]) and sex as covariates. Linear complete case regression models were performed, and β-coefficients and 95% confidence intervals were reported.</p> Results <p>Five hundred fifty-one families of CSHCN (68.24% female; 44.46% aged three to six and 34.66% from seven to ten years old) were available for analysis (10.99% missing outcome). CASP total mean score was 75.99 (± 20.03; range: 25–100), the lowest in living activities subscale (68.07 ± 24.81), including household activities, shopping, transportation. In the complete case regression analysis (<i>n</i> = 350), older child age and higher HRQoL were associated with higher social participation score across all domains. Children with both physical and cognitive impairments had lower CASP scores in the total, home, and school models, with a trend to association in the community model. Lower parental educational attainment was significantly associated with reduced social participation in the living activities subscale.</p> Conclusions <p>In this study, we confirmed previous findings on factors determining social participation in CSHCN, such as age and higher HRQoL. Impairment complexity (combined physical and cognitive impairments) decreased participation in home and school. The lower participation in daily living activities for lower educated parents confirms, that social environment significantly influences social participation. This highlights that to improve social participation, strategies are needed that address family-level <i>and</i> broader environmental barriers to lessen social and functional disadvantages in particularly vulnerable subgroups.</p> Trial registration <p>PART-CHILD cohort, German Clinical Trials Register - Deutsches Register Klinischer Studien (DRKS), DRKS00015054, registered on 16 November 2018.</p>