These stories are so funny! DH and DS6 both have giant heads. My MIL often tells the story about when the delivering doc saw DH's head, he started to tell MIL about his concerns over the size of it, and then he looked up at MIL's giant head and said, "Oh, never mind."
DS6 has worn the same hat size as me for the past couple of years (avg. size adult). We've almost always made our own Halloween costumes, so the big head hasn't been a problem. Last year, DS was a totem pole, this year he's still undecided. A couple ideas he's thrown out - Perry the Platypus from Phineas and Ferb or a Hex Bug.
