Well, the X-Men's franchise isn't the most faithful to original source of the world.
X-Men (2000) has Iceman as a young boy, said that the First Class is composed by Cyclops, Jean, Storm and Beast. These are the most notable.
X2 (2003) has still Iceman and Pyro as young boys, Stryker is a soldier and the man behind Wolverine's origins. These are the most notable.
X-Men: Last Stand (2006)...well...this is all wrong! XD
Wolverine (2009) has mutants appeared in the Wolverine's past...And they're wrong (Why Gambit?). And most of notable: Deadpool...Oh man...
But now X-Men: First Class seems more faithful. Why? Because it seems will be based on "X-Men: Deadly Genesis" by Ed Brubaker.
This story arc shows the real origins about X-Men and the real...First Class! In the comic we see a young Xavier and a young Moira. Xavier has a secret and formed a First Class with mutants like Darwin, Sway, Petra and Vulcan.
The story is set in the past, when Cyclops and Jean are babies. And yes: Emma Frost is a young lady, part of Hellfire Club in this comic. In this story we see also Banshee.
I don't know how of this comic will be put in the movie but it seems more believable and faithful. In the comics we see a third brother of Cyclops from past; I think Singer and Vaughn changed this and substitute the character with Havok.
So, it seems logical and faithful. And surely in the second one we'll see the Second Class (like in the comics!): Cyclops and Jean...
More info: http://en.wikipedia.org/wiki/X-Men:_Deadly_Genesis