I claim the ornamental design for a portable toilet for child, as shown and described.
FIG. 1 is a collapsed view of a portable toilet for a child; and
FIG. 2 is a partially exposed view of a portable toilet for a child showing the disposable bag for disposing of human waste or the washable container for waste disposal home use; and
FIG. 3 is a left side view of a portable toilet for a child with the disposable bag for disposing of human waste in place in the portable toilet; and,
FIG. 4 is an image of the portable toilet for a child in use by a child.
The broken line showing environment is included for the purpose of illustrating a portion of the toilet that forms no part of the claimed design.