Helmets are a much tougher proposition. Good ones don't come in 'adjustable' or 'one size fits all'. I've got some old 'ajustable' ones from back in the day, but the only 'safety' they provide is getting you 'safely' past the ranger's inspection. I think some of the Protek helmets have liners that can be changed to fit different sized melons. Go for the larger sized helmets and just tell the 'pinheads' to wear a baseball cap underneath it.
BoaterTalk 
