In this study, we investigated children's classroom engagement and disaffection and their relationships with class size, child gender, child age and school type in Vietnamese kindergartens. Children's classroom engagement and disaffection were examined among 1315 kindergarteners (mean age = 5.49; SD = 0.87) and 33 teachers from 31 classrooms in 8 kindergartens. The results of confirmatory factor analyses indicated that children's classroom engagement and disaffection included four dimensions: behavioural engagement, emotional engagement, behavioural disaffection and emotional disaffection. The results also showed that both behavioural and emotional dimensions of classroom engagement were higher than those of disaffection. Girls had higher emotional and behavioural classroom engagement and lower emotional disaffection than boys. Class size had a negative relationship with both dimensions of children's disaffection. The findings also indicated that children in the older age group showed greater emotional disaffection and lower emotional engagement compared to children in the younger age group.