I was told by one of the parents who was a medical practitioner herself and had done a huge amount of reading and discussing it with clinicians etc, that it is unhelpful for other adults to affirm the gender identity thinking it was kind and the best approach was avoiding using affirming language and to treat the name change as being a nickname. I was told the very same thing by another of the mothers. She told me just how hard it was to maintain a neutral approach when well meaning adults used affirming language and how ingrained it had now become in her daughter because of that language usage.
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My daughter didn't get as far as actively identifying as a boy (or non-binary) but every time someone asked her her pronouns, generally out of kindness, I could see that she moved a little closer to doing so. On one occasion when she was asked, when she was actively gender questioning, she said she wasn't sure but was leaning towards he/him.
She still gets mistaken for a boy now, because of her short hair, height and clothing choice. She still uses a nickname that sounds neutral, although she uses a different one (that sounds female) at home. I've lost count of the number of times that I still need to say to well-meaning adults that it's unhelpful conflating her lack of "gender conformity" with gender identity. That it's just a nickname etc. When I mention that autism can lead to discomfort with puberty, and that conflating this with gender identity adds confusion, this does tend to open up the conversation in a positive way. I've only been told by a couple of people (so far) that my views are awful.
When people do ask her her pronouns, she tends to say "I don't mind"... which almost always seems to lead to people saying "they". Again, I have found myself having to find an opportunity to say, without my daughter there (i.e. from a safeguarding perspective) that "they" suggests that she is neither a boy or a girl and that this too is also unhelpful. Thankfully, as she has got older, she is starting to feel clearer on what it means to be male and female.