I'm sorry but the parents of that four year old child are idiots.
There is no all encompassing definition as transgender.
Gender dysphoria is a real and crippling thing. Generally it is understood that it kicks in at puberty but I'm willing to believe it may kick in earlier (Fish).
It is located in exactly the same part of the brain that anorexia is.
We don't tell anorexics that by some fluke of biology it's a shame they haven't been born skeletal. We don't tell trans-able people that mother nature has done them a huge disservice by giving them four healthy limbs, and not letting them be born a quadriplegic.
The 'girls like princess dresses, boys like pirates' thing is a huge red herring. At least three quarters of the women on here know that their children (and they themselves) have flipped between gender norms and it means nothing.
This study showed absolutely no brain difference between adult transwomen and males. There was no 'freminisation' of their brain.
It DID show a difference in the trans-women that was located in the area of the brain connected to gender dysphoria ( and anorexia, - dissatisfaction with body parts/image) The study did not prove whether or not the gender dysphoria was innate, or simply a consequence produced because the subjects 'ruminated over their bodies'.
Personally I think it was already there because why ruminate for no reason?
It's a psychological issue. It is compounded because late transitioning males, who have autogynephilia, like to encourage the 'born in the wrong body' narrative from a very early age as it lends credence to the ideology.
No one is born in the wrong body. It's scientifically untenable. People have gender dysphoria and it should be treated with any means possible.
It does not mean that boys are girls, or men are women. You cannot change sex. And telling tiny children that they can is setting them up for a lifetime of confusion, medical intervention and misery. However they feel, they cannot change sex.
digest.bps.org.uk/2011/11/02/male-to-female-transsexuals-have-male-brains/