<p>Children with moderate-to-profound intellectual disabilities face substantial and cumulative exposure to adversity, yet the developmental timing, accumulation, and resilience processes shaping their lives remain poorly understood. This qualitative multiple-case study examined the experiences seven families through a life-course lens. Data included semi-structured parent interviews, a brief orally administered adversity checklist, and multidisciplinary case files. Analyses reconstructed family trajectories across six developmental phases and examined cross-case patterns. Adversity was frequent, layered, and prolonged across medical, caregiving, relational, and systemic domains, typically beginning prenatally. Additional exposures clustered at transitions and intensive contacts, and burden was higher when services were fragmented or poorly matched. Many stressors originated in medical or family circumstances. The organization and continuity of care also shaped how adversity accumulated and was managed over time: when care was relationally attuned, collaborative, and responsive to individual needs. Parents described enduring experiences of living loss, grief linked to altered milestones and ongoing medical risk, alongside continuous efforts to sustain resilience in everyday family life. Resilience emerged as a dynamic, co-produced process supported by children’s sociability and perseverance, parental advocacy and attunement, and stable, proportionate supports (e.g. day services, respite). Cross-phase matrices and cross-case synthesis from the interview–checklist–file triangulation enabled a developmental reconstruction of how adversity and adaptation evolved across family, clinical, and service contexts. with parents preferring an interview-first sequence. These analyses showed phase-specific clustering at transitions and organization-dependent load, refining conceptualizations of adversity and identifying practice priorities for trauma-aware, family-centered care that support resilient functioning.</p>