The ornamental design for the portable playpen for infants, as shown and described in the drawings.
FIG. 1 is a perspective view of the portable playpen for infants of this
invention. FIG. 2 is a left side view of the portable playpen for infants
of this invention; and, FIG. 3 is a top view of the portable playpen for
infants of this invention. The three other side views (right, front, and
rear) are identical to the left side view of FIG. 2. The bottom view does
not form a part of the design of the invention. The elements shown in
broken lines are for illustrative purposes only and form no part of the
claimed design.