Communicating climate risks to vulnerable groups motivating them to take adaptive actions remains a significant challenge in many populations, especially to children. The theory of reasoned action (TRA) suggests that attitude and subjective norms are important for persuasive communication. This study assesses how to apply TRA, its constructs and other relevant factors to predict behavior intention and beliefs and to change behavior tendency. The randomized field experiment method was applied to explore the differences between pre- and post-communication treatments (2 × 2 design). Can Tho city, located in the Mekong Delta of Vietnam, was selected as the research context because of its vulnerability to climate change. The results show that, first, TRA was found to be a significant predictor model of children’s climate change behavior intentions. Second, attitude has a significant effect on the children’s intention to act while videos with subjective norm treatment had not. The treatment interaction of both constructs also had a significant effect. Third, TRA theory-based treatments are positively associated with changes in children’ salient beliefs on attitude and normative belief on social norm toward climate change. In addition, past practices, knowledge and gender are further factors that influence children’s behavior intentions. A theory-inspired design of communication strategy allows the prediction and influencing of intentions. This finding has strong implications for both research and development in Vietnam.