A child safety seat assembly for use in a rear facing position. The child safety seat assembly includes: a child safety seat, and a base portion, to be placed on a vehicle seat and for holding the child safety seat. The base portion includes at least one rail, a pair of ISOFIX latches, connected to the at least one rail and for connecting the base portion to the vehicle seat, and a sledge connected to the at least one rail and for holding the child safety seat. The sledge is, with the child safety seat mounted thereon, movable along the at least one rail such that the position of the child safety seat is adjustable when the child safety seat assembly is connected to the vehicle seat.