Sitting postures and comfort experience were analysed from six children aged 7‐9 (131‐145 cm) seated on an Integrated Booster Cushion (IBC) and a high‐back Booster (hbB) during 1 hour on‐road drives, respectively. Data were collected from video recordings, questionnaires and interviews. When seated on the IBC the most frequent posture was with the entire back and shoulders against the seat back and the head upright. On the hbB, the shoulders were seldom against the backrest. The most frequent lateral sitting posture for both boosters was upright with the seat belt in contact with the neck or mid‐shoulder. Moderate and extreme forward and lateral postures occurred occasionally. A positive attitude was found towards the IBC due to possibilities to move freely, the soft seat cushion and the absence of torso supports, but the short seat cushion created some inconvenience. The hbB was perceived hard, created a locked‐in feeling and felt unpleasant due to movements when changing postures. The combination of objective and subjective measures provided valuable information regarding children’s sitting behaviour. It is obvious that children do not always sit in on‐road drives as in crash tests. Their activities and perceived discomfort influenced the selection of sitting posture and seat belt positions.