without reading all of the responses, I would say there is a huge difference between accepting a child and allowing them to do whatever it is they think they want to do at a young age. I don't think that at that age they have it all sorted out and can truly be certain. I would let my child know that I accept him as he is, that I was fine with him/her cross dressing, adopting a different name to reflect his preferred gender, etc. I would not support hormones or surgery at a young age, but would let my child know that I would fully support that once he becomes an adult, if he so chooses to go that route. I have a few reasons for that decision.
1. Kids question. It's natural. Often the child will do a 180 in a years time, but drastic changes are permanent. Clothing can be taken off, names reverted back to what they were, etc., but surgery and hormone treatments are permanent. It's an adult decision and the individual needs to be an adult to make it.
2. They are still physically developing. We don't know what effect messing with their hormones during such a developmental period could do to them. The consequences may not be as intended. I could not elect to do something that has that much potential to harm my child.
3. Jr. high/high school is hard enough without the kid getting ridiculed for having had surgery. again this is a permanency thing. Once it is done, going back doesn't work so well. But if you crossdress and the ridicule is too much, you can always stop crossdressing, and wait until a calmer time of life to go through with it.
Like I said, accept the child, respect his feelings, discuss his options, but let him know that things that require an adult signature need to wait for his adult signature.