Gender identity is not the same thing as sex.
Gender has to do with the physical/chemical makeup of the brain while sex is your chromosomes.
People realize that transgenders actually have brains that more closely resemble that of the opposite sex than their own, right?
So a MTF transgender is someone who might have been born a male but have a brain that resembles that of a natural born female. It's not as simple as "he likes to dress in girl clothes" or he's feminine so he's a transgender. It means that their actual brain is telling then they're a girl because they have brain that is built more like that of the opposite sex.
That being said, I don't think a six year old is at an age where the brain is developed enough to actually be a transgender but science and our knowledge of it is constantly evolving so I tend to keep an open mind about this.
A lot of excuses for foul, disgusting behaviour and attitudes.
Gender isn't physical now?
Male brains in a female body and vice versa?
Your brain tells you nothing, you control what you think upon and act upon. If your "brain" is tellin you fairy tales about what you are, why continue to believe it?
Not only that, fixing their brain chemistry to match their physical gender is a more rational and healthy attitude for gender/sexually confused individuals.