We had a friend come to TITP with us the other day and he needed a hat, so I found a little pattern & tutorial online from Whitney Sews, and this is how it turned out. I tried finding some period pictures of boys' caps to try and recreate, but didn't have a lot of luck, so I just had to make do with this. Funny thing was, on the way to our house when I was sewing this, the friend stopped at the store and found a darling hat to wear. Luckily, I spent only about 30 minutes making the cap (didn't line it).
This is slightly big on me, but fits my son pretty well. Maybe our heads are about the same size now?