Parents have very important role in giving children early sex education. Early sex education given will influence children behaviour in the future and children will misinterpret sex should they lack knowledge on sex. Objective : This research aimed at finding out parents’ demography characteristic and the level of knowledge on sex education for children at SD Negeri Ngrukeman. Research Method : The type of the research is descriptive quantitative and the sample of the research were 64 respondents from Grade IA and IB students of Sekolah Dasar Negeri Ngrukeman with total sampling technique. The analysis used was descriptive in the form of frequency and percentage. Research Result : The result indicated that the level of parents’ knowledge on sex education for children in good category was 50 people (78,1%), in medium category was 11 respondents (17,2%) and in poor category was 3 respondents (4,7%). Conclusion and suggestion : Most parents were included in the good category in the knowledge of sex education for children so that the researcher suggested that it was necessary to do further research on the way parents give children sex education at early age.