Alright, I thought I'd share this, since a lot of CMs don't seem to be aware of it.
I tried on a hat, and it was small, but I really, really wanted it. I also saw 2 people try them on, say they had big heads, and leave. I commented to the CM who was ringing me up that I usually wear child's ears, but this was small. She told me they come in sizes, and voided the transaction while I went to find another hat.
There were 2 CMs roaming the store (Elias & Co) making displays of 3 small hats on top, and a bin of both sizes below. I must have seen 8 people some in, try on one of the small hats from the display, put it back and walk away. I figured out that if you lift the Disney label, there is a size label underneath. I found Sm/Med hats, which are really small, and LG/XL hats, which are pretty big. Anyway, it's too bad Disney hasn't hired me on commission, because I went through the bins for awhile (looking for the perfect hat, a lot of the ears went floppy and the badges are crooked.) and I told at least 20 people about the sizes. I made so many sales!