This fits my 7 year old nephew perfectly. You can add or subtract rows on the hat base increase rounds to adjust the size of the hat.

The Chain 2 at the beginning of each row does not count as a double crochet.
When you fasten off, be sure to leave tails long enough to sew the items on to the hat. (You can also just weave in your ends and use a separate strand of yarn to sew the decorations on.)