The ornamental design for a childsafetyseat, as shown and described.
FIG. 1 is a perspective view of a child safety seat showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof;
FIG. 8 is a perspective view thereof with the upper portion pulled up; and,
FIG. 9 is another perspective view thereof with the upper portion pulled up.
The dashed broken lines illustrate portions of the child safety seat that form no part of the claimed design. The dot-dash broken lines define the bounds of the claimed design that form no part thereof.