Fold the sheet over with right sides together and the large hem at the bottom.
Fold the pants in half at the back seam and lay the seam on the fold of the sheet, and the bottom aligned with the sheet hem.
Use a pencil to outline the pants, about 1 inch away from the edge of the pants.
Cut out the pants from the pencil tracing.
Fold the sheet over again with right sides together and use the first pant panel cut-out to cut a second panel. The two cutouts will act as the front and back of the pajama pants.
Pin the two cut-out pants together with the right sides facing.
Sew a 1/2 inch straight seam along the outer sides and the inner sides of the legs.
Clip the curve along the crotch seam area.
Fold 1/4 inch of the top of the waist and press.
Then fold 1 inch of the top and press again to create a waistband.
Sew the waistband down at the bottom edge.
Cut the elastic to fit your waist.
Pin one end of the elastic with a safety pin and use the pin to guide the elastic through the waistband.