Background <p>Childhood obesity is a global public health concern. In Ireland, the age standardized prevalence rates for obesity in children and adolescents are about 1% higher than the average for countries in the WHO European Region. The Parents Plus Healthy Families program (PP-HF), an 8-week, group-based, multicomponent parent training intervention, was designed to prevent childhood obesity by helping parents promote healthy habits within their families.</p> Methods <p>A multisite cluster randomized controlled trial was conducted to investigate the effectiveness of the PP-HF program across 16 community-based and clinical settings. Sixty-eight parents were assigned to the PP-HF group and 70 were assigned to the treatment as usual (TAU) control group. Parents completed measures assessing healthy habits, child lifestyles behaviors, parental lifestyle-specific self-efficacy, parental satisfaction, family dysfunction, and child behavior problems at baseline and post-intervention. Parents in the PP-HF group completed measures at 6-weeks follow-up.</p> Results <p>Multi-level modelling analyses demonstrated that post-intervention, compared to the control group, parents in the PP-HF condition reported significant improvements on measures of healthy habits, parental satisfaction, family-functioning, and child behavior problems. Gains were maintained at 6-weeks follow-up. No change was observed on measures of child lifestyle behaviors, or parental lifestyle specific self-efficacy compared to the control group.</p> Conclusion <p>The PP-HF program may be effective in improving healthy habits, parental satisfaction, family functioning, and child behavior problems among families with children aged 2–12 across both clinical and community settings.</p> Trial registration <p>This trial was retrospectively registered on Open Science Framework on 11.^th April 2023. Registration DOI: <a href="https://doi.org/">https://doi.org/</a><a href="https://doi.org/10.17605/OSF.IO/4PY63">https://doi.org/10.17605/OSF.IO/4PY63</a></p>