Avoiding injury and ensuring safe evacuations of children in disasters has always been a central issue requiring close attention in policymaking. However, there is little behavioural data on children's evacuation on stairs. In this study, evacuation drills were conducted in a three-storey kindergarten in Dalian, China. The article explores the well-trained children's vertical evacuation behaviour on stairs and horizontal evacuation behaviour in other areas such as corridors and lobbies. According to the vertical behavioural evacuation data collected in this study, the mean speed of children aged 4–6 is 0.55 ± 0.12 m/s, and children of different age groups exhibit distinctive evacuation behaviours on stairs. The mean speed of children on a horizontal plane is 0.87 ± 0.22 m/s. Then, the relationship between behavioural data (movement time, density, velocity, and flow rate) is compared and analyzed. It is found that the density and flow rate of the crowd at the stairwell entrance and the exit are higher than that of adults, and the children's walking speed is relatively slow. This study can provide reference for safety design, evacuation strategies and evacuation simulation settings of multi-storey kindergartens.