Background. Childhood overweight and obesity is a public health epidemic with far-reaching medical, economic, and quality of life consequences. Brief, web-based interventions have received increased attention for their potential to combat childhood obesity. The purpose of our study was to evaluate a web-based, maternal-facilitated childhood obesity prevention intervention dubbed Enabling Mothers to Prevent Pediatric Obesity Through Web-Based Education and Reciprocal Determinism (EMPOWER), for its capacity to elicit sustained effects at the 2-year postintervention follow-up mark. Method. Two interventions were evaluated using a randomized controlled trial design. The experimental, EMPOWER arm received a social cognitive theory intervention (n = 29) designed to improve four maternal-facilitated behaviors in children (fruit and vegetable consumption, physical activity, sugar-free beverage intake, screen time). The active control arm received a knowledge-based intervention dubbed Healthy Lifestyles (n = 28), which also targeted the same four behaviors. Results. We identified a significant group-by-time interaction of small effect size for child fruit and vegetable consumption (p = .033; Cohen’s f = 0.139) in the EMPOWER group. The construct of maternal-facilitated environment was positively associated to improvements in child fruit and vegetable behavior. We also found significant main effects for child physical activity (p = .024; Cohen’s f = 0.124); sugar-free beverage intake (p < .001; Cohen’s f = 0.321); and screen time (p < .001; Cohen’s f = 0.303), suggesting both groups improved in these behaviors over time. Conclusions. The EMPOWER arm of the trial resulted in an overall increase of 1.680 daily cups of fruits and vegetables consumed by children, relative to the comparison group (p < .001, 95% confidence interval = [1.113, 2.248]). Web-based maternal-facilitated interventions can induce sustained effects on child behaviors.