A child safety seat has a seat back (16) with an upper end (28), a lower end, a back side, and a front side (26). A harness (50) has a pair of shoulder straps (58) each having a portion positioned forward of and extending along the front side. A headrest (32) is coupled to the seat back near the upper end and has a bottom (40). The vertical position of the headrest is selectively adjustable along the seat back between a raised and a lowered position. A strap router (112) on the seat back directs the shoulder straps from the back side toward the front side. The shoulder straps are directed under the bottom (40) of the headrest. By selectively adjusting the headrest vertical position, the bottom (40) of the headrest adjusts the vertical position of the shoulder straps on the front side of the seat back by increasing or decreasing the useable length.