Help resizing this hat pattern?

I am IN LOVE with this hat and I desperately want to make it for two children in my life, both of whom are two years old. Unfortunately the instructions make a hat to fit a 4-8 year old and I have no idea how to resize it. Any help resizing the pattern or a link to a similar hat that has instructions for a smaller size would be GREATLY appreciated. I am dying to make this hat!

Here is a link to a pdf with the free pattern:

The hat measures just under 18" and you need about an inch or two less than their heads measure. So get that measurement first. It’s possible you could use sportweight yarn and size 6 needles. If you can knit up a sample to get your sts/inch and see if 81 sts would come out about the right measurement you need. If that works, just follow the pattern. If size 6s are too big, try 5s.