The ornamental design for a child-friendly stethoscope chestpiece, as shown and described.
FIG. 1 is a perspective view of a child-friendly stethoscope chestpiece showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines immediately adjacent the shaded areas represent the bounds of the claimed design, while all other lines are directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design.