Calorie labeling is now required on all large U.S. chain restaurant menus, but its influence on consumer behavior is mixed. This study examines whether different parent-targeted messages encourage parents to order lower-calorie meals for their children in a hypothetical online setting. An online RCT was conducted with diverse primary caregivers of children aged 6–12 years (data collected and analyzed in 2017–2019). Participants (N=2,373) were randomized to see 1 of 4 messages: (1) nonfood control, (2) kids’ meals are the right size for children, (3) doctors recommend a 600 kcal per meal limit for kids, or (4) 600 kcal per meal is a generally recommended limit for kids. Participants ordered hypothetical meals for their children and themselves and rated meal and message perceptions. There were no significant differences between conditions in calories ordered for children at either restaurant, although all 3 food message conditions ordered fewer calories for their children than the control (full service: 27–68 fewer kcal, fast food: 18–64 fewer kcal). The general 600 kcal/meal limit message consistently performed best across outcomes, encouraging parents to order the fewest calories for their children at both restaurants (5%–7% fewer) and significantly increasing their understanding of calorie recommendations for kids’ meals. It also significantly reduced fast-food calories parents ordered for themselves compared with the control (−106 kcal, p=0.042). Although no statistically significant differences were detected, messages with specific calorie recommendations for kids led parents to order lower-calorie restaurant meals for their children, suggesting that additional real-world studies with larger sample sizes are warranted.