How to make a Mermaid tail in less time than it takes to watch Frozen!

Materials required
A piece of stretchy fabric big the length of your childs waist to toe measurement plus enough foe seam allowances -jersey will be fine
Heavy weight iron on interfacing
elastic - enough to go around your childs waist - I used 1" elastic
Cotton
sewing machine
overlocker/serger - if you have one
Frozen DVD