Emergency braking can influence children’s posture and seatbelt interaction. To better protect children in crashes preceded by emergency braking, this study aims to quantify kinematics and seatbelt engagement during braking events. Eighteen rear‐seated children were exposed to braking events with 1 g deceleration in a passenger vehicle, restrained by the seatbelt on a booster cushion and an integrated booster cushion. Vehicle acceleration and video data were analysed to measure head displacement and shoulder belt position. On the booster cushion the belt was generally mid‐shoulder and lower on the torso with a gap, while on the integrated booster cushion it was closer to the neck and higher on the torso without a gap. Average forward head displacement was 160 mm on the booster cushion and 150 mm on the integrated booster cushion. Generally, the belt maintained the same position on the shoulder throughout braking, with exceptions influenced by shifted initial positions or non‐standard motions. Braking events placed the head approximately 150‐190 mm forward from the initial position, influenced by booster, stature, and initial seatbelt positioning. This reinforces the importance of maintaining mid‐shoulder or close to neck belt positions and upright, centred postures prior to emergency braking, which may influence the likelihood of impacting the vehicle interior and sustaining head injuries in a subsequent crash.