A child safety seat for use in a vehicle has a seat body (10) and a harness (16-22) including a pair of shoulder straps (16, 18) which extend through respective slots (28, 32, 36) in the seat back (26) to a mechanism for adjusting the length of the shoulder straps (16, 18). The height at which the shoulder straps (16, 18) project from the seat back (26) can be varied by threading them through different slots. A pad (50) is slidably mounted on each shoulder strap (16, 18) and has a cover formed of high friction material on the side (52) thereof facing the child occupant's body. A tether strap (54) has one end attached to each pad (50) and projects through the same slot (28, 32, 36) in the seat back (26) as the corresponding shoulder strap (16, 18) for limiting movement of the corresponding chest pad (50) along the shoulder strap (16, 18) to a predetermined limit distance away from the seat back (26). Such limit distance increases as the height at which the shoulder straps (16, 18) project from the seat back (26) is increased.