Meh, they're fine as they are !
No need to copycat America.
Agreed. I don't particularly relish the idea of being surrounded by kids in a film that would otherwise be rated 15 or 18. The restriction is there for a reason, if they make it so that anyone can go into a "16A" rated film as long as they're accompanied by a person over 16 then it kind of defeats the object of even having an age rating.