I know there are tons of sewing tutorials about installing elastic, but figured out a way that I love. It's very similar to installing elastic on swimsuits. (Maybe that's why I love this so much, because I LOVE making swimsuits!) I thought if I loved this method so much, there might be someone out there that can benefit too!
A half-finished pair of pants/shorts/skirt
1. Finish the top edge of your pants, either serge, zigzag, or fold over.
2. Try the half-finished pants onto you or your child. Fit the front part of the pants snugly and then measure the distance needed around the back. My son's is 6".
3. Add 1/2" to the measurement and cut that from elastic. Wider elastic is better to use.
4. Sew the elastic ends at the side seams. It's alright if stitching shows because it will be folded over.
6. Stretch and pin until the elastic is distributed evenly across the back.
7. Sew down the center of the elastic with either a serpentine or a zigzag stitch from side seam to side seam stretching as you go. Don't worry, this stitch will only be seen on the inside of the pants.
9. Sew all the way around the waistband 1/8" from the elastic. (My elastic was 1", so I sewed 1 1/8" around the waistband.) You will have to stretch the back as you sew. Feel free to add multiple lines of stitching on the back over the elastic; I find this gives a great manufactured look.