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 = 0.033; 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 = 0.024; Cohen's f = 0.124); sugar-free beverage intake (p < 0.001; Cohen's f = 0.321); and screen time (p < 0.001; 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.