Effective interventions are needed to address the growing epidemic of childhood obesity. In the past 35 years, family-based approach has gradually developed as a preferred intervention. This review aimed to examine the methodological rigour and treatment effectiveness of family-based interventions according to intervention types and theoretical orientations. A total of 15 randomized controlled trials (RCTs) of family-based lifestyle interventions for children and adolescents aged 2–19 years were included. The adapted Methodological Quality Rating Scales (MQRS) and a four-grade qualitative scoring scheme were adopted to evaluate the methodological rigour and the effectiveness of treatment, respectively. The average MQRS score was 7.93 out of 14 points. Ten of the 15 RCTs had well aligned their research questions with appropriate research methods. The overall short-term outcome of the15 RCTs were satisfactory with an average score of 3.1. Family-based interventions rooted in behaviour theory achieved better results than those theoretically connected to family systems theory in terms of treatment effectiveness. Results suggest future studies to improve the methodological design and continue to explore the potential of the family systems approach.