Nominally Karma was the leader, at least. Whilst she was the oldest of the group, she was still a teenager, and needed some adult guidance. Thats where Professor Charles Xavier came in, apparently bored of his original X-Men now they were adults himself. Instead he busied himself with forming a new group of wayward, superpowered sprogs. Kind of a jerk move, but what more do you expect from the guy. It remains to be seen if Xavier makes an appearance in the film (and whether hell come in McAvoy or Stewart flavour), but he was rather integral to the early days of the team. Which is to say, he made them keep to a curfew and trained the other psychics. Of course, the films might always take a different path, and follow the example of the Ultimate X-Men series. Set in an alternate universe, the Ultimate New Mutants were lead by a much more chilled-out, less murderous Emma Frost. Who, in that continuity, was a former lover of Professor X. Hey, that Days Of Future Past retcon couldve changed a lot of things...
Tom Baker is the Comics Editor at WhatCulture! He's heard all the Doctor Who jokes, but not many about Randall and Hopkirk. He also blogs at http://communibearsilostate.wordpress.com/