The pattern is adult size, if you are a firm knitter you can use needle #3 instead of # 2,5. If you will like to make it smaller, just cast on 18 stitches less than original, that will work just fine, then you just might have adjust a bit on how long you knit the hat, for a child I would knit 6 cm instead of 10 cm after the increasing.

You will need two skeins of the main colour, and one with colour #2.