FIG. 1 is a front perspective view showing my new design for a booster seat, FIG. 2 is another front perspective view showing a strap in an alternate position, FIG. 3 is a top view thereof, FIG. 4 is a bottom view thereof, FIG. 5 is a front view thereof, FIG. 6 is a rear view thereof, FIG. 7 is a left side view thereof; and, FIG. 8 is a right side view thereof.