Abstract: A device for positioning a slidable crib rail including a sliding rail having an upper and a lower locating hole, and an upper and a lower arresting block located closer to an end of the sliding rail than the upper and the lower locating hole respectively. The device also includes a moving member for positioning the crib rail along the sliding rail. This moving member includes a control member having a retaining device retaining the moving member in the locating holes of the sliding rail, and a movable plate having a first position for biasing the retaining means in a position in which the retaining means cannot retain the moving member in the locating holes and a second position which does not influence the retaining means. The upper arresting block of the sliding rail is situated to move the movable plate from its second position to its first position, and the lower arresting block of the sliding rail is situated for moving the movable member from its first position to its second position.