[Rie]

Here's a knitted acorn hat pattern.
http://www.ravelry.com/patterns/library/acorn-hat-5

I agree with ArtLady about converting a pattern. If the texture of the hats you linked to is what you like, I'm not sure you'll find it in an easy knitted hat pattern. Any knitted beanie with color changes will give you an acorn hat.

If you have your heart set on one of the hats in yout links, you might have to learn to crochet as well as knit.

I think this is an excellent pattern choice. He could also knit up a few of the leaves in fall colors that salmonmac suggested as add-ons. The leaves would be good practice before starting on the hat.