Next, determine which side will be on the outside versus the inside of the fabric. With the right sides together, pin in place.
Sew 3 sides of the body sock leaving a ¼ inch seam allowance using the zigzag stitch (my stitch length is 1.5; stitch width 3.0), leaving one short side open. Make sure to gently guide the fabric through, do not pull. Secure seams by backstitching. Sew the corners using 90 degree turns, do not curve your corners. The open short side will be used for the opening for the head. We will close the shoulders later.
Make sure both layers of fabric are sewn in place on both sides. If needed, resew those areas making sure to backstitch.
Next, turn the body sock right sides out through the opening. Push the corners out. Have your child try on the body sock, and make sure it's a good fit.
Next, to close the shoulders, carefully pin or hold in place. I held the fabric around the shoulders in place, 3 inches in from the corner seam. This allowed the child to get in and out with ease while also providing deep pressure around the shoulders. Make adjustments based on your child’s size. Carefully remove body sock, maintaining hold or pins indicating where to sew. Pin the shoulders in place if needed.
Lastly, turn the body sock back inside out before sewing the shoulders, and close the shoulder area by sewing in place making sure to backstitch.
Next, reinforce any high stress areas such as the corners continuing to use the zigzag stitch. Trim any loose ends using scissors.
Turn right sides out, try on again. The body sock should hold in place around the shoulders while the child can still easily get the body sock on and off.
Done! Inspect the seams regularly in case you need to restitch over certain areas.