Here is a beautiful rose headband design that is very easy to make. It's based on granny square pattern, which most crocheters have mastered even as beginners. The headband tapers off in the back, and you can easily adjust the placement of the button for a perfect fit. As far as the length goes, you can always add or subtract a couple rows to make a desired size change. I give my suggested sizes for a toddler, a child and an adult.
Skill level: beginner to intermediate
Finished dimensions: sized for toddler (about 19 inches), child (about 20 inches) and woman (about 22 inches).
Yarn: worsted weight yarn - about 1.5 oz main color (MC), 0.7 oz complimentary color (CC).
Hook: size 9 or I (5.5mm) or size to obtain gauge.
Other materials: tapestry needle, 3/4 inch button.
Gauge: 18 dc and 9 rows = 4" (double crochet)