I love this pattern for a little boy. The diamond is so easy and fast to do, and looks perfect for a boys hat. This is light weight and can be worn summer or winter.

basic measurements:
12 months to 3 years=circumference 18” to 20” Hat height=8”
3 years to 10 years=circumference 19” to 20 1/2” Hat height 8 1/2”.