Background <p>Japan’s child-welfare system prioritizes returning children to their birth families when safe (“reunification first”). In this context, infant homes (nyuji-in)—residential out-of-home care settings for infants and toddlers—are increasingly responsible for coordinated support for children and families with complex needs, including those without formal diagnoses. However, few studies examine how these institutions address such needs.</p> Objective <p>This study examines how Japanese infant homes coordinated observation-driven, diagnosis-independent, developmentally responsive care for infants and toddlers identified as children with special health care needs (CSHCN) and how they supported families across entry, in-facility care, and transition/post-care phases.</p> Methods <p>A qualitative multiple case study was conducted in three nyuji-in functioning as comprehensive support centers. One illustrative case per facility was purposively selected from children meeting ≥ 1 criterion on the CSHCN Screener, based on staff observations and records. Data included institutional records, growth and developmental charts, and semi-structured interviews with staff and caregivers (<i>n</i> = 14 across three cases). Analysis followed Yin’s explanation-building approach, guided by domains from a scoping review on psychosocial and care support for CSHCN and by Ziring et al.’s care coordination framework.</p> Results <p>Three cross-case themes emerged: tailoring care to complex and evolving needs, coordinating transitions through interprofessional and interagency collaboration, and sustaining relational continuity to promote family engagement. Across cases, teams prioritized observation-driven responses and adapted plans collectively, with or without formal diagnoses.</p> Conclusions <p>Infant homes may function as adaptive hubs for multidisciplinary care. Implications include structured follow-up, caregiver engagement, and pathways toward stable reunification or foster placement.</p>