For Child:
Knitted Cast On 51
K2TOG to join in round, place marker at beginning of round (50 sts)
Knit 10 rows.
Purl 3 rows
Knit 3 rows

Setup for decreases:
(K 10, place marker) repeat to end of round

Decreasing:
Row 1: (K to 2 sts before marker, K2TOG) repeat to end of round
Rows 2-4: Purl
Row 5: (K to 2 sts before marker, K2TOG) repeat to end of round
Rows 6-8: Knit

Continue decreasing this way until 10 stitches remain, knitting through row 8 of the Decrease pattern. Then repeat rows 5-8 one last time. (5 sts remaining)

I cord finish:
Knit 1, K2TOG, K2TOG (3 sts)
I-cord for 3 rows
K3TOG
Weave in ends!

For teen and (adult):
Knitted Cast On 56 (61)
K2TOG to join in round, place marker at beginning of round (55 sts (60 sts))
Knit 13 rows.
Purl 3 rows
Knit 3 rows

Setup for decreases:
(K 11(12 for adult), place marker) repeat until end of round

Decreasing:
Row 1: (K to 2 sts before marker, K2TOG)repeat to end of round
Rows 2-4: Purl
Row 5: (K to 2 sts before marker, K2TOG) repeat to end of round
Rows 6-8: Knit

Continue decreasing this way until 10 stitches remain, knitting through row 8 of the Decrease pattern. Then repeat rows 5-8 one last time. (5 sts remaining)

I cord finish:
Knit 1, K2TOG, K2TOG (3 sts)
I-cord for 3 rows
K3TOG
Weave in ends!

I have only knit the Child size of this, so my numbers for the adult and teen may be wrong.
Child Hat wearble depth, unstretched: 7”
Child Hat from unrolled brim to tip: 12”
Child Finished unstretched interior diameter: 17”