Objective  To determine the efficacy of a family-involved hand washing intervention on the improvement of hand hygiene of children and the prevention of infectious diseases among children in kindergartens.

  Methods  A cluster-randomized controlled trial was conducted among 490 children (averagely aged 4.28 ± 0.33 years) and their parents at 16 classes from 4 kindergartens in Guangzhou city from March to June in 2018, and there were 8 classes in each group by randomization. Totally 247 children and their families were enrolled in the intervention group with family-involved hand washing intervention, and 243 children and their families in the control group with regular health education. The behavior of hand washing among the children and their parents and the incidence of infectious diseases of children between the two groups were compared.

  Results  Hand washing behaviors of the children were significantly different between the two groups after the intervention (hand washing before eating b = − 0.207, after toilet use b = − 0.106, after going out b = − 0.149, and with seven-step procedure b = − 0.113; all P < 0.05). The hand washing before eating, after toilet use and going out, and with seven-step procedure 2 months after the intervention, the hand washing before eating 4 months after the intervention, and the hand washing before eating and with seven-step procedure 6 months after the intervention were significantly better among the children of intervention group than among those of the control group (all P < 0.05). The hand washing of the parents in the intervention group were significantly better than that of parents in the control group 2 months after the intervention (hand washing before eating χ² = 8.750, after toilet use χ² = 7.243, after going out χ² = 15.557; all P < 0.05). The cumulated incidence of acute gastrointestinal and respiratory infections was significantly lower among the children in the intervention group than among those in the control group (9.3% vs. 16.0%, χ² = 5.031; P = 0.025) during the 12-month follow-up.

  Conclusion  The family-involved hand washing intervention is effective in improving hand hygiene behaviors among kindergarten children and their parents and reducing infectious diseases in the children, suggesting that the intervention is of significance for infectious disease prevention in kindergartens.