You can use one color of yarn or two colors of yarn to crochet this hat. This hat is loose at the top. If you want to crochet warm hat, you should use a thicker yarn. If you want to crochet lightweight summer hat you should use DK weight yarn and crochet loosely.
Size:
1 - 3 Years - Circumference of the head 18” - 19”
3 - 10 Years - Circumference of the head 19” - 20.5”
Adult Small/Medium - Circumference of the head 21” – 22”
Material and tools:
100 - 130 g any worsted or DK weight yarn: approx. 218.7 yards (200m)/100g.
Crochet size H (5 mm) hook, size E (3.5 mm) hook.
You can use multiple strands of the yarns to make up a single strand of worsted weight approx. 280m/100g.

Stitches and Abbreviations: (US terminology)
Single crochet – sc Chain – ch
Double crochet – dc Yarn over – yo
Slip stitch – sl st Cluster double crochet together - cluster dc tog
Round(s) - rnd(s)