I hate to say it, but mumsnet is an extremely hateful place when it comes to trans rights. you're going to get some really biased opinions on here.
There's no hate. What there is is realism and caution. The medical transing of children is an ethical minefield and imo is going to be a far, far bigger medical scandal than Thalidomide.
Mumsnet is a parenting site. How many parents would want follow a course of action that can lead to their child becoming a lifelong medical patient, or being sterilised?
Medical treatment of gender dysphoria is immensely harmful. Puberty blockers and cross sex hormones will sterilise a child before they're old enough to vote.
By contrast 80% of children managed by watchful waiting will grow out of their gender dysphoria once puberty is past. Most of these children turn out to be gay or lesbian. Members of staff at the only NHS gender clinic for children have said that medical transition of these kids is a form of conversion therapy - transing the gay away.
Human beings can't change sex. There's no getting round that. Surgery and medication can create features that copy the opposite sex but it's seldom very convincing, though FtMs are more likely to pass.
But it's not something anyone would choose unless they absolutely had to. Transgender people find their pool of potential partners is very much reduced and their health is compromised, sometimes significantly.
If a parent can support their child to overcome this phase then of course they should. And it's very definitely a phase. In one school a dozen girls in one year group identify as boys.
When I was young it was eating disorders. More recently it was cutting. Now it's binding and gender dysphoria. I'm not discounting the genuine anguish behind these fashions but there are definitely fashions.