Purpose: This research aimed to evaluate the biomechanical impact on a 3-year-old child's head during collisions with unmanned aerial vehicles (UAVs), focusing on the effects of UAV mass, impact velocity, and impact direction, using the Head Injury Criterion (HIC) for assessment. Methods: Experiments simulated impacts with UAVs of varying masses (249, 500 and 900 g) and velocities (19.0, 24.0 and 29.0 m/s) from different directions. HIC values were measured for each scenario and analyzed in relation to the Abbreviated Injury Scale to determine potential injury severity. Results: The findings showed that both the UAV's mass and impact velocity have a significant influence on the HIC value, with higher figures indicating a greater risk of serious injury. For the UAVs weighing 249 g and 500 g, frontal impacts resulted in the highest HIC values; however, for the UAV weighing 900 g, the highest HIC value occurred for the back hit. Moreover, injury risk was found to escalate non-linearly with increased velocity, especially for heavier UAVs. Conclusions: The study emphasizes the critical influence of UAV mass and impact velocity on the severity of head injuries in children. Increased mass and velocity correlated with higher HIC values, indicating a greater likelihood of severe injury. Frontal impacts were particularly hazardous for lighter UAVs, while rear impacts were more dangerous for heavier UAVs. These findings support the need for stringent regulations on UAV operational parameters, focusing on speed and mass limitations, to mitigate the risk of severe head injuries in children.