Six years old is a little too young for that. You never truly know the reasons for the child "wanting" this. It could simply be that they truly want it, OR it could be very bad parents forcing the child to say that they want it. 6 years old is just too young.
I don't know, as a member of the LGBTQ community, I have much difficulty understanding the "T" part. I can only offer my experience. I pretty much knew my sexual preference by age 11. But at age 6??? I don't recall having the foggiest notion. I do recall that I was an effeminate child. However, if my parents had misconstrued it and went through these drastic measures to reassign my gender, I would have despised them for it. However, that is just my case.
From what I read so far in this case, it appears the child may be "gender expansive." Whatever that means. I'm not certain taking steps to force the child to be a "girl" is the called for action here.