Yet not BEFORE the 1930s because hormones did not exist before the the 1930s which disproves your entire "always been here" argument dumbass.
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It is
very unlikely that these children - Mark and David Ferrow/Marjorie and Daisy Ferrow - were trans teens who got to transition in 1936. The first known case in the UK of someone attempting to help someone transition was Dr. George Lush Foss in 1939 in Bristol, who gave Michael Dillon testosterone tablets because, as you note, hormones had basically only just been discovered. The first trans phalloplasty in the UK was performed on Michael Dillon in 1946 (which involved falsifying paperwork). There certainly wasn't a hospital in London that would help teenagers transition through hormones and surgery. The first hospital for that in the UK was Charing Cross Hospital in the 1960s, and it wasn't until 1989 that a clinic opened for trans kids (the Tavistock).
That all being said, in the 1920s and 30s, the Charing Cross Hospital did have a specialist who focused on children with disorders of sexual development (a lot of trans clinics grew out of endocrinological specialists focusing on DSDs). Lennox Broster started his practice there in the late 1920s. Frequently it was misreported he was "helping people change sex", but more accurately it would be said he was performing (agreed to) "corrective surgery" and hormonal treatments on individuals with DSDs - for example the female athlete Mary Weston, who became Mark Weston and resulted in gender tests coming into women's sports.
Mark's sister Hilda also became Harry through Lennox Broster's work, which does hint at some sort of congenital DSD along with Mark's own testimony. It's worth noting that in this era, it was a lot more common for doctors to "guess" wrong with ambiguous infants and particularly to recommend male infants be raised as girls if the genitals were very small. The idea that this could have been incorrect was not actually as controversial as you'd think.
Anyway, if we dig out the original version of the carefully cropped image from that magazine article;
[Marjorie] noticed her voice was cracking just like those of the neighbor boys her age. It was getting deeper and losing much of its soprano quality... Marjorie was much disturbed. She left school and no amount of urging could persuade her to return.
Daisy's voice too, began doing the strange antics when she reached 13... so doctors were consulted.
Marjorie (was) sent to a London hospital to find out what was wrong... The doctors had discovered that a great biological change had been going on ever since her voice gave her such distress.
Finding another article:
In those four years they had undergone a sex change... Mark was operated on at a London hospital to complete his transformation. David has yet to undergo an operation. According to medical records, the case of Mark and David is unique.
So very clearly both children began experiencing a male puberty when they came of age, at odds with the idea that they were girls. This was not because of them taking hormones, it was because they had a disorder of sexual development, which (probably) Lennox Broster treated with additional hormones and surgical interventions. So, not transgender, probably something like 5 alpha-reductase deficiency (like Caster Semenya) or PAIS.