I have a small head too. Bell small helmets are smaller than the other selection of helmets I've tried on a Performance. While you can get helmets with adjustable plastic things on the rear of the helmet, I still want a helmet that mostly fits my head instead of being held in place.
And you know what? Kids helmets aren't any smaller than adult helmets! I would love to have a bright green helmet with dinosaurs on it! Any Universal fit helmet is a FAIL. I don't know if anyone makes helmets in XS, but I've never seen any.