The ornamental design for a child's bootie, as shown and described.
FIG. 1 is a front right side perspective view of a child's bootie, embodying my new design;
FIG. 2 is a left side elevational view thereof;
FIG. 3 is a right side elevational view thereof; and,
FIG. 4 is a bottom view thereof.
A characteristic feature of my new bootie is the exclamation mark design on the bottom of the bootie, as shown in FIG. 4.
The broken line showing of the stitching to secure closures is included for the purpose of illustrating environmental structure and forms no part of the claimed design.