Design by Crochet 365 Knit Too.
This pattern shows you step by step on how to do the math in order to crochet this to any size you need from child to adult. As for the flower, you can use it on hats and bags as well.
You will need a button to attach to the band. The flower then slips over the button, thus allowing you to crochet flowers in all colors for a new look each day.
As for yarn and hook size, you can basically use anything that you have on hand.