<p>This study aimed to validate the Chinese version of the Beach Center Family Quality of Life Scale (BCFQoL) and examine how parent–child divergence in perceived Family Quality of Life (FQoL) impacts child quality of life among economically disadvantaged families in Hong Kong. A cross-sectional survey of 242 child-parent dyads was conducted (September 2023–2024). The BCFQoL was validated using confirmatory factor analysis (CFA) with robust fit indices among samples of children and parents. T-test was used to examine the significant divergence in FQoL perceived by children and parents. Response surface methodology (RSM) was employed to analyze the effects of divergence among child-parent dyads on child quality of life. The BCFQoL demonstrated strong psychometric properties, supporting a higher-order model where four dimensions, i.e., family interaction, parenting, emotional well-being, and material well-being, collectively predicted overall FQoL. Children reported significantly higher FQoL than parents across all domains (<i>p</i> &lt; 0.050). RSM revealed that child QoL improved with higher child-reported FQoL, regardless of parent perceptions. Congruence at high FQoL levels was ideal, but incongruence where children’s perceptions exceeded parents’ still associated with better outcomes (<i>b</i>_<i>1</i> = 0.582, <i>p</i> &lt; 0.001 for overall FQoL). This study validated the Chinese BCFQoL among child-parent dyads with a hierarchical four-factor structure and investigated the divergence in FQoL perceptions between children and parents and its effects on child quality of life. The findings inform policymakers to prioritize multi-informant assessments and programs that amplify children’s narratives to mitigate intergenerational stressors.</p>