Maternal substance use is a pressing public health issue that confers risk for maternal health, the parent-infant relationship, and child development. Integrated interventions that jointly address maternal substance use and child development have shown promise for enhancing child outcomes. No research to date has focused exclusively on the outcomes of young children or examined potential moderators of the effect sizes of integrated programs. This review evaluates the pooled effect of integrated interventions for substance-involved mothers on the developmental outcomes of their children. A comprehensive search strategy was conducted in seven databases (APA PsycINFO, CINAHL, Cochrane CENTRAL, Embase, MEDLINE, Sociological Abstracts, Web of Science) from January 2011 and May 2023. Studies were included if they reported on an intervention with at least one substance use treatment and one parenting or child treatment service for substance-involved mothers of children under 6 years of age. A total of 21 studies met inclusion criteria, and 14 nonoverlapping studies reported on effect sizes with a pooled effect size of SMD = 0.470 (95% CI = 0.35, 0.59). There was a trend toward treatment duration being a significant moderator (p = 0.08). Additional high-quality studies are needed to demonstrate the long-term impact of these interventions.