Abstract: This sitting unit comprises a central part (5) articulated on the front edge of the sitting unit and thus raisable forwards, a receptacle (7) designed to receive this central part (5) when it is turned down into the sitting unit, and a device (8, 8a, 12) for locking and retaining in the raised position the central part, to the rear face of which a child's seat can be attached. This arrangement increases the safety of the child in the event of a front collision of the vehicle because the child's seat faces rearwards, instead of facing forwards, so that, in the event of a collision, the child is already steadied in the seat and does not suffer the injuries caused by the belts which are conventionally used.