Measure the length and width of your crib (mine was 52 1/2″ long and 26 1/2″ wide). Height doesn't matter because we're going to cut all pieces to 11″ high. This height seems to be about average for a crib bumper pads.
Cut batting in the exact width and length of the crib (I cut 2 pieces of batting to 52 1/2″ x 11″ and 2 pieces of batting to 26 1/2″ x 11″).
For all four sides of the crib bumper pads, pin the batting to the corresponding fabric layers with the fabric layers on bottom. You'll notice that the batting is 1/2″ shorter than the fabric layers. This is intentional to leave a 1/2″ seam on one end, which you will slip-stitch later.
For each of the crib bumper pads' four pieces, sew three sides with 1/4″ seams. Leave open the end where the fabric is 1/2″ longer than the batting.