I really love the effect of the mosaic crochet technique. If you’ve never tried it really is a simple technique.
The rounds are made up of sc’s that are worked into the back loop of the st you are working on, which leaves the front loop of that st available to work a dc into. The dc will be worked into the front loop of the row below you are working on, the dc you are making and the row below is the same color, so it’s easy to know where you are working into.

This hat can be made in many sizes, from new born to large adult using a stitch count in multiples of 8.
You can also use a thicker yarn and larger hook.
Once the band has been made and joined for the size of your hat, the 1st row of the body of your hat will be adjusted for the pattern stitch count.