["Applied Psychology: Health and Well-Being, Volume 18, Issue 3, June 2026. ", "\nAbstract\nGuided by the Positive Youth Development (PYD) framework, this study shifts the focus from a deficit‐based view to a strengths‐based perspective by examining how ecological assets and internal strength collaboratively shape the developmental trajectory of loneliness among rural left‐behind children. Specifically, the study examined whether different dimensions of social support (i.e., emotional support, instrumental support, companionship, enhancement of worth, and intimacy), conceptualized as ecological assets, were related to loneliness trajectories, and whether resilience, conceptualized as a key internal strength, played a longitudinal mediating role in these associations. A three‐wave longitudinal survey was conducted with 517 Chinese rural left‐behind children (53.77% boys; Mage = 12.69, SDage = 1.52) over 10 months (designated as T1, T2, and T3). The results indicated that instrumental support at T1 negatively predicted the initial level of loneliness and positively predicted the decline rate of loneliness, while intimacy positively predicted the initial level of loneliness. The initial level of resilience mediated the negative associations between instrumental support and enhancement of worth at T1 with the initial level of loneliness. These findings highlight the person–context interplay in rural settings, suggesting that strengthening instrumental support and enhancement of worth, while fostering early resilience, is crucial for promoting adaptive development among left‐behind children. The study advances the PYD literature by demonstrating how children's strengths can be mobilized to navigate the challenges of parental absence.\n"]