In Hong Kong, as elsewhere across East Asia, few empirical studies have captured the voices of children in their middle years to analyse the determinants of subjective child well-being. To fill this research gap, this article employs data from 1,279 randomly selected Hong Kong children aged from 9 - 14 to investigate the mediating role of social capital in the relationship between their socioeconomic status (SES) and subjective well-being. The data was collected as part of the third wave of the International Survey of Children’s Well-Being which included Hong Kong for the first time. Using a path analytical framework and bootstrapping analysis as part of a theoretical ‘health assets approach’, several sub-components of social capital, including family, school, and community sense of belonging as well as peer relationships, were found to constitute protective factors for Hong Kong children’s overall life satisfaction (OLS) as well as their scores on the multi-item Children’s Worlds Subjective Well-Being Scale (CW-SWBS). After controlling for SES and other sociodemographic characteristics, family, school, and community autonomy support were not found to augment the subjective well-being of Hong Kong children. Furthermore, school sense of belonging augmented children’s scores on the composite CW-SWBS but not OLS. This article adds to the literature by presenting empirical evidence that a strong sense of belonging—particularly but not exclusively within children’s families—and strong peer relationships present valuable social resources that can be utilised by children in their middle years to optimise their subjective well-being irrespective of their family socioeconomic background.