I drew a pattern on a big sheet of paper and cut it out.
Then pinned it to the fabric for the tails. We were making 5.
Once we had the 2 sides cut out we turned them inside out and sewed all but the top edge.
Then turned them right side out and ironed them flat.
We only had 3 beach towels so we cut them in half and folded over and finished the unfinished edge. The towels were big, and the girls were small enough that half a towel was long enough for them. We just sewed the tail onto the bottom edge of the towel.
We measured the girls and sewed two pieces of velcro onto each towel.
Here's the finished product.
I put them in their party favor buckets.
The girls were stoked on their mermaid tails!