It's a shame (but sadly not a surprise) to see the word "transphobia" on this thread. Unfortunately it's impossible to call out the risks of children identifying as the opposite sex, non-binary, furries, therians (or any other identity) without someone thinking this is transphobic.
I don't believe that everyone has a gender identity. However, I accept that many people do believe this and that some people who do will feel incredibly distressed that their perceived identity doesn't match their body. Anyone in this situation deserves evidence-based healthcare care to support them. I also don't believe in god, but I accept that many people do and that for them their faith impacts many aspects of their lives.
Perhaps I'm both transphobic and Christianphobic?
some of the vocabulary is reminiscent of when it used to be acceptable to think being gay was just a phase.
Some people ignorantly used to think, some still do, that being gay was a phase. Also, some people unfortunately just are homophobic.
There is a world of difference between a child starting to wonder if they might be gay and a child starting to wonder if they might be "in the wrong body" (e.g. transgender or therian/other-kin identity). Unfortunately all of it has been conflated and muddled together under LGBTQ+, making it very confusing for adolesents to navigate during the emotionally turbulent time of puberty.
unless you start doing extreme genetic testing on everyone, you can’t just rule that all trans women are men.
Another unfortunate conflation is when DSDs are brought in to the mix.
Everyone is either male or female (their sex) and DSDs are sex-specific.
It's impossible (not just an outlier) to have a womb and a penis, owing to the order in which reproductive organs are formed. Everyone starts with "bi-potential gonads". In males, the instruction (the SRY gene, normally on the Y chromosome) tells the body to form testes from these gonads - from this moment on, it's impossible to have a womb. The lack of this instruction (the lack of an SRY gene) tells the body to form ovaries from these gonads - from this moment on, it's impossible to have a penis. Reproductive organs always form in the same order: testes or ovaries first, then the internal "plumbing" (womb etc or prostate etc) until finally the external features (vulva/clitoris etc or scrotum/penis).
Although all DSDs are rare, one of the more common in males is "46 XY 5-ARD". In this DSD, the penis and scrotum don't form until puberty. Everything else is formed inside as normal but the external genetalia look "female" at birth. When they get to puberty, boys with 46 XY 5-ARD will find that their body finally reacts to the SRY gene: their voices will drop, they will grow a penis and (most of the time) their testicles will drop outside the body. They are no different to any other male at this point, with male strength and speed etc - although many will have grown up believing themselves to be female, which must be very confusing and distressing to go through. From what was written in the press, it sounds like the two Olympic boxers at the heart of this year's controversy had this condition. Sometimes the testes might stay inside e.g. the runner Caster Semenya talks about having internal testes.
This is a brilliant, compassionately written article about 46 XY 5-ARD by Michael Moseley a few years ago:
https://www.bbc.co.uk/news/magazine-34290981
However, as has been said by PPs, all transwomen are males i.e. they have been born with male body parts, male strength and speed etc. Some may end up removing body parts but, according to Stonewall, most retain their penis and testicles. It's impossible to be a transwoman unless you are a male.