Before I start let me state that I am very much for transsexual rights .
Boston Children's Hospital is now offering sex change clinics for children as young as seven. That is something I believe to be a very big mistake. Yes children can feel as though they are in the wrong gender body from a young age, but the decision to change their sex should not be allowed until at least the age of sixteen. Transforming from one gender to another does make an immediate and very potent change on one's life. It is a decision that shouldn't be allowed at a time in life when the world is quick to judge you, especially peers. The harassment that could easily come with the decision, because peers are not open minded to such things, could be devastating to the way the child grows and develops. They could easily become depressed, suicidal, or even violent towards others. I would say the age of sixteen to be the youngest point you can decide that because at that point you can look at the good things that would come of it, but also the many negative reactions you will get from close minded society.
If I was a psychologist I would have much more to say on the matter. Children's minds have not even developed enough to understand what comes with a sex change.
Also in some ways being gay or trans gender is a fad, and what do kids to? They try to be cool. They could try so hard to be cool, convince their parents they really want to change sex, and realize later that they made a really big mistake, that they liked their original sex.