Nobody can 'change sex'. One is born with either XX or XY chromosomes, and nothing can alter that

While that may be the scientific definition, I doubt if anyone posting here has decided on the sex of the majority of the people they meet based on a genetic analysis. So to me that doesn't really address the question. The social aspect is what is being considered here.

I have a close relative who is transgender. And she is far happier and more sociable than he ever was. Just about every one of my relatives who I have spoken to about it has been perfectly comfortable and only distressed at all my the main decades of misery he endured in fear we could not accept it.

As far as children are concerned, I would be extremely wary but not totally opposed. There are cases as well where the gender is physically indeterminate and some decision has to be made: in those cases at least it is sensible the child is involved.