This beanie can be adjusted to child to adult size by changing the two stitch repeat cast on for the brim.

You can change the hook size down to a US H / 5.0 mm - US I / 5.5mm for a child beanie using the same stitches for the brim.

Use worsted weight yarn - same yarn weight may have different variation and feel thinner.

You will use one skein
If you want the brim color to be different you will need 18 grams.