Measure the mat or cot your child will be using in her preschool class, using a measuring tape.
Choose a flat twin-size bedsheet to use for your child's cot. Your child can choose a sheet with her favorite cartoon characters or in her favorite color. Try using a flannel sheet for added durability.
Cut the sheet to match the measurements of the preschool mat or cot exactly. Since there is minimal sewing to this method, you need to make sure you cut the sheet to the exact measurements of the cot. If you would like to sew, leave a half inch or so on each side of the sheet to create a hem.
Apply the fray-stop spray on each end of the mat sheet to help keep fraying to a minimum. You may need to repeat this process a few times during the school year, as frequent washing may cause the sheet to fray a bit on the edges.
Measure and cut four pieces of elastic to place in the corners on the back side of the sheet. Place the elastics at a diagonal, creating a triangle on each corner of the sheet. When sewn, these elastics will slip over the back of the mat and hold the sheet in place securely.
Secure each end of the elastic in place at the edge of the sheet using a needle and thread. You may also use a sewing machine with a wide zigzag stitch to secure the elastics to the sheet.
Slip the elastic loops over the back side of the preschool mat or cot in order to secure the sheet.