Background <p>Instrumental activities of daily living (IADL) limitations reduce the well-being of older adults. However, it remains unclear whether co-residence with children or other family members provides sufficient support to mitigate this impact. This study examined the longitudinal effect of IADL limitations on well-being and assessed whether the presence of children or other sociodemographic characteristics moderated the relationship.</p> Methods <p>821 participants from waves 4 and 5 of the Indonesian Family Life Survey were analyzed. IADL limitations were measured by the presence of difficulties in shopping, preparing meals, and taking medicine. Well-being was assessed by a composite index combining happiness, self-rated health, and depressive symptoms. Living arrangements were classified based on household composition. An asset index was built by applying tetrachoric principal component analysis (PCA). Ordered logistic regression models were used.</p> Results <p>IADL limitations in wave 4 (AOR 0.41, p-value 0.003, 95% CI 0.23 0.75) and worsening IADL limitations over time (AOR 0.50, p-value 0.000, 95% CI 0.36 0.70) were independently associated with poorer well-being in wave 5. Higher levels of household assets (AOR 1.67, p-value 0.003, 95% CI 1.19 2.34) were significantly associated with good well-being. The decrease in assets over time (AOR 0.62, p-value 0.003, 95% CI 0.45 0.85) was independently associated with poorer well-being. No significant interaction effect was found between IADL limitations and living with adult children (OR 0.41, p-value 0.014, 95% CI 0.20 0.84) or other household members.</p> Conclusions <p>Co-residence with children or other family members does not appear to mitigate the adverse effects of IADL limitations on the well-being of older adults. Instead, policies aimed at strengthening financial adequacy and maintaining functional capacity could be more effective in enhancing their well-being.</p>