The topic in the OP is not reassignment surgery. It's gender identification.
There was some reference previously made regarding chemical alterations to prevent puberty. If you are satisfied allowing a child to roleplay (lack of a better word, not intended to be offensive) their way through the teenage years before making serious choices, I'd have no issue with that. I previously posted about a woman I knew in junior/senior high that was adamant she was gay. Everyone believed her. I did. Imagine my surprise when I met her husband at the class reunion...
Sometimes children make choices for various reasons that are not always rational. Sometimes there is influence pulling the strings. If there was a genetic marker we could point to and say "opps.. mother nature screwed this one up in processing" it would be one thing perhaps. But as is, I think taking things slow is the best bet.
Even if with that said, I do not feel it is fair to force everyone around these individuals to live in the manner as they see fit. I've worked in a facility with a transgender person. The women that used to be put off by the crude/rude individual he was before, now get to share restroom facilities with this person. Is that fair? Never mind the impending threat of action anytime she gets her feelings hurt because someone didn't respond when she attempts making small talk and gets offended. Some people (especially older generations) have a real difficult time dealing with these types of issues. Tolerance and professionalism is something everyone has the right to expect. Acceptance is not.