The ornamental design for a child's bib, as shown and described.
FIG. 1 is a front plan view of a child's bib according to my new design, showing an indicia thereon marking a particular location and a neck opening proximate to the top of the bib for accepting a child's neck;
FIG. 2 is a rear plan view of the bib showing a pocket at a location opposite the location of the indicia on the front of the bib;
FIG. 3 is a side view of the bib as seen from the right in FIG. 1;
FIG. 4 is a top view of the bib; and,
FIG. 5 is a detailed view taken from FIG. 1 of a closure for the neck opening, showing Velcro® fastening strips on mating sides of flaps on the neck opening.