An child vehicle seat comprising a back support, a seat portion, a crotch member extending through the seat portion, as well as belts that can be detachably connected to the crotch member for securing an child in the child seat. The belts extend through the back support and are connected to at least one tensioning belt on a side remote from the seat portion, by means of which the belts can be tensioned in a tensioning direction. The tensioning belt extends under the seat portion towards a locking mechanism, which, in a locking position thereof, locks the tensioning belt against movement at least in a direction opposite the tensioning direction. The locking mechanism can be moved to a releasing position by means of the crotch member, in which position the tensioning belt is movable in the opposite direction of the tensioning direction.