Objective: To understand the proper handwashing behavior of preschool children and primary school students in Beijing, and to analyze associated family factors to provide reference for further health intervention related to handwashing. Methods: From November to December 2020, parents of 36 kindergartens and 18 primary schools in 9 districts of Beijing were investigated online by using a self designed questionnaire with questionnaire star software. The contents of the survey included the basic situation of children and their families, parents correct knowledge of the prevention of novel coronavirus pneumonia, their perception of the epidemic risk, the provision of handwashing guidance for children, and children s handwashing behavior. Results: The proportion of proper handwashing of preschool children was 70.2%, which was higher than that of primary school students (61.9%) ( χ 2=57.63, P <0.01). The proportion of parents of preschool children who correctly knew handwashing related knowledge (36.2%, 33.4%), had low perception of epidemic risk (28.9%, 25.4%), and provided handwashing guidance (99.1%, 97.9%) was higher than that of parents of primary school students, and the differences were statistically significant ( χ 2=6.72, 22.84, 18.68, P <0.05). But the proportion of parents of preschool children who had high self efficacy (75.7%, 78.2%)was lower compared to parents of primary school students( χ 2=6.43, P =0.04). Multivariate regression results showed that whether preschool children or primary school students, urban areas and parents had high self efficacy, low risk perception, and provided hand washing guidance for children, children were more likely to wash their hands correctly. For preschool children, non only children were 0.79(95% CI =0.69-0.92) times more likely to wash their hands correctly than only children. For primary school students, girls were 1.21(95% CI =1.06- 1.39 ) times more likely to wash their hands correctly than boys, and parents who know knowledge correctly were 1.20(95% CI = 1.04 -1.40) times more likely to know it incorrectly( P <0.05). Conclusion Proper hand washing behavior of preschool children is higher than that of primary school students. Parental awareness of COVID-19 epidemic, handwashing behavior, self efficacy and guidance behavior have effects on the development of children s health behavior. Measures should be taken to enhance parents awareness of infectious diseases and their ability and self efficacy of guiding children in disease prevention.