A child safety seat has a seat back and a seat harness with a pair of shoulder straps. Each shoulder strap has a strap portion positioned forward of and extending along a front facing side of the seat back. A headrest is coupled to the seat near an upper end of the seat back. The vertical position of the headrest is selectively adjustable relative to the seat back between a raised position and a lowered position. A strap router is provided on the seat back and maintained at a fixed elevation relative to the seat back as the vertical position of the headrest is adjusted and directs the shoulder straps from a back side of the seat back toward the front facing side. The shoulder straps are directed under a bottom of the headrest. By selectively adjusting the vertical position of the headrest, the bottom of the headrest adjusts the vertical position of the shoulder straps on the front facing side of the seat back by increasing or decreasing the useable length of the strap portions.