The present study investigates the mechanisms underlying the relationship between parental depression and children’s smartphone addiction. It explores the effects of parental depression on children’s smartphone addiction, as well as the mediating roles of parental neglect and children’s self-esteem in this relationship, which multiplies sequentially. We utilize data—comprising 2,396 children and their parents—from the National General Survey on Korean Children, using parent–child dyads. First, a hierarchical regression analysis shows that parental depression significantly and positively predicts children’s smartphone addiction ( B = .29, SE = .03, p < .001). Second, Hayes’s PROCESS macro (Model 6), executed to test the mediation effects, reveals that the effect of parental depression on children’s smartphone addiction is significantly mediated by parental neglect ( B = .07, Boot SE = .01, 95% Boot CI [.05, .10]) and children’s self-esteem ( B = .12, Boot SE = .01, 95% Boot CI [.10, .14]). Moreover, the serial mediation model’s results support that parental neglect and children’s self-esteem serially mediate the relationship between parental depression and children’s smartphone addiction ( B = .02, Boot SE = .004, 95% Boot CI [.01, .03]), implying that a higher level of parental depression is sequentially associated with increased parental neglect that reduces children’s self-esteem and consequently accelerates their smartphone dependence. The theoretical and practical implications of the results as well as the directions for future research are discussed.