During emergency evacuations, children sometimes adopt three-dimensional (3D) motions, such as crawling close to the ground or climbing up/down to obstacles, to pass through restricted spaces or in situations of heightened urgency. Examining how these motions affect children’s evacuation performance is essential for designing effective behavioural instructions. The present study examines the influence of 3D motions on the efficiency of children’s indoor evacuations. A simulation framework is applied, combining a voxel-based 3D indoor representation with an agent-based behavioural model. Detailed scenarios are elaborated to account for different agent numbers, urgency levels, and physical attributes. The work is presented as an exploratory case study, not as a validated replication of real-world evacuation drills. The results indicate: 1) The use of 3D motions is relatively low across all urgency levels and agent numbers. 2) The number of agents moving above or below indoor objects slightly increases with higher urgency and more agents. 3) 3D motions may not significantly influence children’s evacuation efficiency due to minor congestion as well as limited use and lower speeds of 3D motions. We recommend refining behavioural instructions by: 1) restricting 3D motions in low-density conditions . 2) Conditional use of 3D motions when local congestion significantly hinders direct evacuation paths. 3) Conduct evacuation exercises tailored to children’s physical and cognitive abilities under specific scenarios. The study contributes to short-term evacuation strategies as well as long-term preparedness and training programmes for children.