The purposes of the study were to explore knowledge and attitudes of elementary school children on sex and gender and needs of the teachers & parents on sexuality education for children in order to develop sexuality education program. For the purposes, we developed questionnaire and implemented to 1,448 elementary students. Also we conducted qualitative interviewing with 27 teachers, 44 students, and 15 parents. The findings are summarized into six items and some implications are discussed. Based on the findings, it is concluded that the content of sexuality education for upper elementary school children should include scientific knowledge and systematic understanding about sex-related physical and mental development, balanced understanding of human relationship, and culture and ethics of sexuality.