This mermaid tail is customizable to be the right size. Mine fits my two year old and also fits my 5 year old with room to grow. It is made larger and then has an elastic waist to fit for play. Pattern has descriptions for how to adjust the pattern for sizing.

Any worsted weight yarn will work just fine. I used Willow Wash in worsted weight for the body of the tail and Caron Simply Soft for the fin and the waist, mostly because I had extra laying around and thought the colors went nicely together. I used about 1.5 skeins of the Willow Wash and 0.5 skeins of the Caron.

You will need an I and J hook. No gauge is given as this can be made to fit regardless of how tight or loose you crochet. It all is based on the starting foundation chain.

Also needed is 1/8” cord elastic (or any thin elastic will work so long as you can thread it through double-crochet stitches) and a needle for weaving in ends.