Need help adjusting hat pattern

I am using silver’s hat pattern:

I am making the hat for my almost four year old. I am using fingering weight yarn on size 1. How many stitches should I cast on?

If I add more stitches where do I need to adjust the rest of the pattern?

Measure his/her head, then subtract an inch or two. Multiply that times the sts/inch you get and that’s the approximate number of sts you need. There’s a 12 st repeat, so you adjust the st number you get up or down so it’s a multiple of 12.