FIG. 1 is a perspective view of a child seat base, showing my design;
FIG. 2 is a perspective view thereof supporting a child seat shown in broken lines, the child seat being for illustrative purposes only and forms no part of the claimed design;
FIG. 3 is a left side elevation view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a front side view thereof; and,
FIG. 7 is a back side view thereof.