Psychologist Freud pointed out that early childhood is the key period of sex education, because it lays the foundation and direction of individual development. Psychologist Kohlberg's research shows that children's gender role consciousness has gone through three stages: gender identity, gender stability and gender consistency, from being able to correctly say "I am a boy" and "I am a girl" to "I am a girl when I grow up" and "I am a girl even if I don't tie my hair or wear pants". It can be seen that although children have not yet entered adolescence, they have learned a lot about sex and gender. Therefore, it is necessary to have sex education in early childhood.

The earlier children receive sex education, the more effective it is to help them stay away from the potential danger of sexual assault. Some studies believe that the education about "sex" received before the age of 5 will undoubtedly determine all aspects of "sex" in a person's life. Some developed countries in the west have realized this and put children's sex education on the agenda very early. British law stipulates that 5-year-old children must start compulsory sex education. In Finland, there are formal sex education books in kindergartens, which carry out sex education from the perspective of sexual health care and strengthen sex moral education. In German, Hongkong and Taiwan Province provinces, we use cartoons or picture books for sexual enlightenment about the birth process of life. Therefore, universal sex education, especially healthy sex education, must start with dolls.