I just noticed a contradiction between what was established in the first X-Men movie and what was shown in X2.
The contradiction involves the boy who could change the channels on a TV across the room by blinking. (For want of a better X-Men codename, I call him “The Channeller”. 
)
This boy was, what? 7 years old? 8 or 9 years old, at most?
Well, in the first X-Men movie, they clearly established that mutant powers don’t manifest themselves until puberty!
Maybe he was an early bloomer. Not everyone reaches puberty at the same time. There are also exceptions to every rule. The kid with the tongue was probably born with it rather than having his human tongue suddenly transform. I realize that comic continuity doesn’t hold for movie continuity, but Nightcrawler has been established as having been born blue.
I wonder how many kids at Professor X’s school are mis-diagnosed mutants. "Well, Timmy, we thought your channel changing ability was a natural mutation, but we just found out that you were bitten by a radioactive cable repairman when you were four. We’re pretty sure that’s what gave you your channel changing abilities. Anyway, we’re transferring you out tomorrow.
True, mutant deformations seem to appear at birth, even while mutant powers aren’t supposed to manifest themselves until puberty. (Nightcrawler wasn’t able to BAMF or cling to sheer walls before he hit adolescence, was he?)
Miller: the X-Universe is rife with that conceptual problem. Why mutants are written as being stigmatized, while the Fantasitic Four or Hulk or even Capitan America, none of whom are particularly any more human in practice than mutants, are not classified as mutants, seems more an element of the decision to put them all in the same universe than it does any coherent cultural concept.
Mutants are born that way, the others acquired their powers by random radiation or super soldier serums. The whole world knows Reed Richards and his crew got their radiation from a rocket trip, and went on to become hip super heroes when there weren’t any, and eventually fought Galactus and won. Captain America is the living legend of WW2. Would you badmouth a guy that fought hitler? (besides Stalin). And the Hulk was wanted by the law when he was a crazy brute (constant army chasing). When he became intelligent, he was no longer pursued by gov’t forces nonstop. Mutants make people afraid because who wants their kid to be born with blue fur?
I believe in the first movie Jean Grey mentions in her speech to congress that mutant powers are brought on during periods of heightened emotion stress, most often during puberty. Therefore if children have a particularly bad experience, perhaps a parent dying or some sort of accident, their powers would manifest themselves early.
well, that kid never sleeps, so he stayed up all night and saw infomertials with Cher and Miss Cleo in them, and that would cause enough emotional damage to make his mutant powers emerge!