I got my nieces measurements which were a 17 in. waist and 6 1/2 in. from waist to knee. I cut a strip of elastic 16 1/2" so that I'd have a half inch to overlap to stitch together. To cut the length I kept the bandana folded in half and cut 8" up from the end. This way it gave me plenty to fold over for the waist.
Pin the two bandanna pieces together wrong side out and stich the two short ends. Then sew down about 1/4" around the waist then turn it down another inch where the elastic will be threaded through. I did not cut any of the width down because I wanted them poofy and girly.
After the waist seams are sewn leave a small opening to pull the elastic through with a safety pin on one end. Stitch the elastic ends together and then hand sew or machine sew the opening together. And all done!
I threw together some headband rosettes with the extra bandanna material so that she has accessories to match her skirts. Every little girl needs plenty of accessories!
***And the best part? Each bandanna was only $1 at Wal-Mart and the elastic was only $1 as well. Two skirts for $3! Can't beat that!