Coping as a mediator between family stressors and behavioural adjustment in siblings of children with progressive life-limiting conditions: a multilevel longitudinal study

Siblings of children with progressive life-limiting conditions face elevated emotional and behavioural risks. Although multiple family stressors are known, how cumulative stress shapes sibling adjustment is unclear. This study examined how illness-related family stressors affect sibling behavioural outcomes and whether active versus passive coping strategies are associated with these relationships.

We conducted secondary analysis of longitudinal data from the Charting the Territory (CTT) study, examining 70 siblings (aged 7–18 years) from 58 families with a child diagnosed with progressive life-limiting conditions. Families were categorized into two treatment-duration groups based on time since first seeking medical treatment for the ill child (≤ 1 year vs. > 1 year). Using multilevel exploratory factor analysis, we empirically derived a latent "Siblings' Stressor" construct from nine potential variables. Multilevel mediation models examined relationships between Siblings' Stressor, coping strategies (Kidcope), and three behavioural outcomes (Child Behaviour Checklist): internalizing, externalizing, and total behaviour problems across baseline (defined as each family's first assessment wave at study enrollment), 6-month, and 12-month assessments.

The Siblings' Stressor construct comprised parental stress, anxiety, depression, and caregiving burden. Significant direct effects emerged between Siblings' Stressor and all behavioural outcomes. Coping associations differed by treatment-duration group. For internalizing problems, active coping provided consistent protection across early (≤ 1 year: -.052, 95% CI [-.103, -.001]) and longer-term families (> 1 year: -.109, 95% CI [-.121, -.097]), while passive coping demonstrated risk effects. However, for externalizing and total behaviour problems, active coping showed different associations by treatment-duration group, being protective in early-treatment families (≤ 1 year) and positively associated with externalizing (.048, 95% CI [.021, .075]) and total behaviour problems (095, 95% CI [.053, .136]) in longer-treatment families (> 1 year). Passive coping was linked to elevated externalizing and total behaviour problems in both groups, with particularly strong associations in families within their first year of treatment.

Parental psychological distress and caregiving burden were associated with sibling adjustment across all behavioural outcomes, with coping strategies showing differential patterns by treatment-duration group. Active coping was related to fewer internalizing difficulties, while passive coping was associated with elevated risk. These findings support family-centred approaches that address parental mental health and promote developmentally appropriate coping strategies across the illness trajectory.