Measure all four sides of the crib from corner post to corner post. The example given here will use 54 inches wide-by-27 inches high for the side rails and 29 inches wide-by-27 inches high for the front and back of the crib.
Cut two rectangular pieces of mesh fabric for each of the above measurements, so there are four pieces total. Add 1 inch to these measurements for seams.
Follow these measurements to cut the hem facing. Cut a double piece for the top of each mesh section, which will be sewn together to make a 4-inch-wide strip for the top. Cut 24 4-inch strips of Velcro tape -- six strips for each section of the mesh.
Sew the 4-inch strips of hem facing for the top of the rails. Use a straight stitch and press the seam closed, with raw edges together. Run a straight stitch along the raw edges, about 1/4 inch away from the initial stitching to help reinforce the seam. Close the ends by turning under a 1/4-inch double hem and stitching it.
Pin the strips of Velcro tape to the hem facing. Secure the tape strips at the top, middle and bottom of the hem facing at the sides of the mesh sections. Sew the Velcro to the hem facing.
Finish the other edges of the mesh with hem facing. Close the ends with a 1/4-inch double hem.
Secure the mesh sections with the Velcro tape. The mesh sections should fit snugly on the inside of the crib.