We have the opposite problem... our craniums are super small! I can actually wear some of DS's toddler size 2-3T hats. Both of my DKs have the same shape and small-sized heads as well. It makes helmets, masks and hats a nightmare!
This year, DD8 wanted to be Anne of Green Gables for Halloween (she read the book this summer and we visited PEI on vacation), but the only family member we have who can sew is away this month. She was disappointed because she had the hat with the braids already. She decided to just be Laura Ingalls, the same as last year.
I am still searching for a Thomas the Train costume for DS2. If I can't find one, he has a super cute Elephant costume that we will use.