BACKGROUND: Text messages improve health outcomes for adults engaged in weight management. Little is known about whether text messaging parents of children enrolled in obesity treatment will improve child health. METHODS: We conducted a 2-group randomized controlled study among 101 children aged 5-12 and their parent/guardian enrolling in tertiary-care obesity treatment. Participants were randomized to standard care or standard care plus daily motivational interviewing-based text messages. The primary outcome was change in child BMI at 3 months. Secondary outcomes included feasibility, health behaviors, attrition, motivation, and parent BMI. RESULTS: We enrolled 101 parent-child dyads and retained 81% to 3-month follow-up. Child participants had a mean age of 9.9 years, and baseline BMI of 30.5 kg/m2. Half (48%) of participants were Black, and 64% of parent participants had a high school equivalent education or less. Ninety-nine percent of parents owned a mobile device with unlimited text messaging. Parents responded to 80% of texts, and 95% felt the texts "always" or "almost always" helped them make a good health decision. We observed no between-group difference in child zBMI from baseline to 3 months (0.0 vs. 0.2, p = 0.2). Intervention participants had significantly better adherence to clinic visits (3.3 visits vs. 2.1 visits/3 months, p < 0.001). CONCLUSIONS: Parent-directed text messages did not significantly change child BMI. However, texting significantly reduced attrition for treatment visits. Nearly all parents in this racially diverse, low-income sample engaged in daily text messaging, making this a feasible approach.