The ornamental design for a blanket for newborns and infants, as shown and described.
FIG. 1 is a front view of a blanket for newborns and infants showing my new design;
FIG. 2 is a back view of thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is a left side view thereof; and,
FIG. 6 is a right side view thereof.
The broken lines illustrate portions of the blanket and form no part of the claimed design. The broken lines along the top end of the blanket as well as along the inner seams of the flat and filled surfaces of the blanket represent stitching, and form no part of the claimed design.