Abstract: A child vehicle seat includes two anchored members secured on a rear side of a back support portion of a seat body and respectively having positioning units, a belt support member movable uprightly relative to the anchored members and having a belt guiding opening, two locking members movable longitudinally relative to the belt support member to engage or disengage two of the positioning units, an actuator movable transversely relative to the belt support member, and a coupling member for transmitting movement of the actuator to the locking members, thereby moving simultaneously the locking members to an unlocking position, where the belt support member is movable uprightly. A belt passes through the belt guiding opening so that movement of the belt support member can permit change of height position of the belt.