A vehicle seat belt system has seat belt webbing that is attached to a tongue adapted to be located in a buckle mechanism fixed to a load-bearing part of the vehicle. A generally vertically extending strap is adapted to be located in a position against a seat back. An adjustable webbing guide connects the generally vertically extending strap to the seat belt webbing; and there is a device for positively locking the webbing guide to the generally vertically extending strap at any one of a plurality of selectable locations on the generally vertically extending strap. A load limiter is operative for a child seat occupant but not operative for an adult seat occupant.