This study explores the prevalence and socio-demographic correlates of depressive symptoms in early adolescents in China, as well as the differences between an only child and non-only child group. A total of 2059 seventh-grade Chinese students were invited to complete a questionnaire, which included questions concerning socio-demographic factors, family function, and the Center for Epidemiological Studies Depression Scale (CES-D). The results revealed the following things. (1) thirty-four point seven percent of the participating Chinese early adolescents display symptoms of depression according to Radloff’s criteria. Differences are significant across the four dimensions (i.e., positive affect, negative affect, somatic symptoms and retarded activity, and interpersonal difficulties), as well as across total scores between only children and children with sibling(s). (2) Academic achievement, having sibling(s) or not, migration, and family function can significantly predict depressive symptoms. (3) Two significant interactions were found, which were between sibling(s) and gender as well as sibling(s) and family function. Girls from the non-only child group and adolescents from the only child group with poor family function were more likely to have depressive symptoms. These findings suggest that a greater focus should be placed on girls from non-only child families, academic under-performers, migrants, and adolescents from poor family environments, and especially only children, to prevent or reduce the propensity for depressive symptoms.