Place the two ribbons evenly on top of each other and center them along one seam on the diaper. Pin the ribbons together onto the cloth. Using a straight stitch on the sewing machine, sew straight along the edges of the ribbon. Fold the ends of the ribbon under until the length of the ribbon is equal to the length of the cloth diaper. Sew completely around the ribbon. Repeat with the remainder of the ribbon along the other seam on the cloth diaper.