Introduction: Weight excess stands out as a major health problem today and its prevention since early childhood is essential for the population health. The use of instructional teaching materials such as flip chart in the educational process in health contributes to the effectiveness of this practice in the service routine. Objective: To develop and validate a flip chart on prevention of childhood weight excess in primary care. Methods: Descriptive study that focuses on the development and validation of an instrument for educational intervention. Honest and wide investigation was developed in the city of Itupeva, State of São Paulo, approved by the Research Ethics Committee and authorized by the city's Health Board. It was developed in three steps: 1) Listening workshops with mothers and health professionals in primary care; 2) Development of a flip chart; 3) Flip chart validation. Based on the theoretical framework of critical education, where three workshops which lasted 90 minutes each were held from April to June 2015: two with 10 mothers, and one with 14 primary care professionals. The workshops were recorded, transcribed and subjected to content analysis. To develop the flip chart, themes were drawn from workshops, technical documents were used from the Ministry of Health and pictures were taken from the internet. The flip chart was validated by eight judges, who were part of the city professional Board of Health and Education. They evaluated the flip chart's content and appearance by filling out a form validation for group discussion. The percentage of the judges' agreement was analyzed. Results: The analysis of the listening workshops gave origin to the topics, "weight excess acknowledgement", "consequences for the child's health" and "strategies for prevention and children's health promotion. The flip chart consists of 27 sheets: odds pages with figure and even pages with plug-Script. There was 99% of the judges' agreement on the proposed theme, 96% regarding clarity and understanding, 94% regarding the importance of each picture, and 47% as for needs of adjustments or exclusion. Resolution improvements and picture replacements were the main suggestions for the material validation. Conclusions: The flip chart construction and validation based on critical education involves the participants, facilitates the use of this technology by health professionals in the educational process in primary care, and promotes understanding and incorporation of important steps to prevent child's weight overflow, contributing to the child's health promotion.