I claim the ornamental design for a children's toothbrush, substantially as shown and described.
FIG. 1 is a perspective view of a children's toothbrush showing my new design.
FIG. 2 is a front elevation view of the children's toothbrush shown in FIG. 1.
FIG. 3 is a rear elevation view thereof.
FIG. 4 is a top plan view thereof.
FIG. 5 is a bottom plan view thereof.
FIG. 6 is a right side elevation view thereof; and,
FIG. 7 is a left side elevation view thereof.
The broken lines illustrate environmental structure and form no part of the claimed design. The different stippling densities used on the different surfaces are included in the drawings to represent the different degrees of shade cast on each surface, e.g., the surfaces facing the light source having the lightest stippling and the surfaces facing away from the light source having the darkest stippling.