Mom, Dad, Sis, Don't read :)
Cut the fabric into bean bag size rectangles- two for each handwarmer. pin the rectangles together, patterned sides facing each other, and sew up three full sides and all but 1 inch of the fourth side. Invert the sewed pouch so the the stitching is on the inside.
To use, microwave the handwarmers for 30 seconds. They should retain heat for about 30 minutes :)