Part of a Children's Cup

FIG. 1 is a front view of a part of a children's cup showing the new design. FIG. 2 is a back view thereof. FIG. 3 is a right-side view thereof. FIG. 4 is a left-side view thereof. FIG. 5 is a top view thereof. FIG. 6 is a bottom view thereof; and, FIG. 7 is a perspective view thereof. In the drawings, even spaced broken lines depict the part of a children's cup that forms no part of claimed design. The dot-dash broken lines immediately adjacent solid line portions of the design depict the bounds of the claim and form no part thereof.