The understanding of sexual education for children aged 5-6 years at RA Nur Kamal has not developed optimally, besides that the media related to sexual education is still limited in its availability. This study aims to develop sexual education using the Sex Education Book media in order to increase the understanding of sexual education for children aged 5-6 years in RA. This study uses the Research and Development method by using data collection techniques in the form of observation, interviews, questionnaires and documentation. The data analysis technique used is descriptive qualitative and descriptive quantitative. The results of this study are a media Sex Education Book that has been declared "Eligible" to be used to improve understanding of children's sexual education, with a feasibility score of 95.75% media validation, 100% material validation, and 100% language validation. User assessment obtained the results of eligibility of 97.22% homeroom teachers, 100% principals, and 100% accompanying teachers. In addition, from the Sex Education Book media trial, it obtained an increase score of 80% and entered the BSB category (Extremely Developed). These results indicate that the understanding of sexual education in children increased significantly compared to the results before using the media which obtained a percentage score of 54.28% in the BSH category (Developing as Expected).