This is in response to the large number of people who seem to get very angry about this topic without really understanding anything about it. Most or many people are happy doing so little reading about transgender issues before forming opinions about them that they don't even read the articles they click on before they comment. They scroll past the text and speedily whip out platitudes and lies that mislead future non-readers of the article into thinking that such statements have anything to do with what's above. When it comes to transgender people, this has the potential to be harmful.
The first myth to get out of the way is that there is a problem with kids being forced into transitions that they regret. Some people have the idea that progressive parents will change the sex of their children the moment they see them playing with the 'wrong' toys, and that lives are being ruined because of this. In reality, even for adults there is nothing quick about transgender healthcare services, and getting any sort of treatment with permanent effects. It seems as though people may be confusing very harmless things such as a child visiting a Gender Identity clinic or being allowed to express themselves through clothing and makeup choices for much more extreme medical intervention with hormones and surgery. People jump into the issue with no idea as to what steps transitioning usually entails, and so I will explain.
Transition for anyone usually starts with some form of counseling, and this may go on for months as it requires you to be very sure about yourself before doctors will be willing to help you go further. Doctors sometimes require that patients live as the gender they identify with by socially transitioning to some degree. Socially transitioning just means expressing yourself differently, changing your appearance superficially, and maybe using new pronouns and a new name. If someone decides that they don't need to transition any further, or decides that they want to go back to how things were before, it will be incredibly simple.
HRT (Hormone Replacement Therapy, to change the balance of sex hormones) is generally the next step, but for kids of age to through puberty, there's a less extreme intervention in the form of puberty blockers. These act temporarily and allow pubescent kids extra time to be sure about their gender identity before they go through either male or female puberty. And for kids who are too young for puberty, there is obviously no need for either puberty blockers or for HRT, allowing them even more time.
Surgeries are even harder to get access to than drugs. SRS (Sexual Reassignment Surgery, to change the genitals) is the most famous, but even for adults this will often come only after years of HRT. Not many surgeons exist who do SRS operations, these operations are expensive, and these operations often require multiple recommendations, time spent socially out, a year on HRT, and so on. In some countries, children are locked out of SRS completely by laws limiting the surgery to those over 18. It is a technical possibility for somebody under 18 to get SRS, but they will first likely spend a long time in counseling, on puberty blockers, on HRT, and presenting as their gender. There are many obstacles before SRS.
(*N.B. Not all transgender people transition, and not all transgender people who transition go through all of the steps listed above. It may not be socially or medically safe for them to transition, or they may just opt out of any number of changes for whatever reason, but they are still transgender.)
Holding all of this in mind, we know now that when people bring up studies that show kids are often okay with their birth sex after visiting gender identity clinics it is not a shocking condemnation of gender identity clinics or medical science. The kids are leaving unchanged and unharmed, and if they are truly not transgender, the clinics probably helped them realize that. In particular, the first choice of reactionaries in the fight against truth is a 1995 study by Zucker and Bradley, a number of 80-90%. This is a low-hanging fruit, but has to be plucked lest someone else uses it as ammunition.
First, the study refers specifically to kids under the age of 8 visiting a clinic. We know, therefore, that these are kids who are not getting SRS, who are not on HRT, and who are not even going on puberty blockers any time soon. Second, if someone goes to a gender identity clinic and then decides they are definitely okay with their birth sex (they are not transgender) before receiving any medical treatment then you might say that paints the current filtering system in a somewhat positive light. Third, the study implied people were okay with their birth sex just because they didn't return for more interviews, regardless of other reasons they may not have returned, or what they might have gone on to do. In particular, these are kids who are still under the control of their parents, many people fall back into denial/ 'the closet' even after coming out once, many people are dissatisfied with official systems, many people don't feel like they need therapy, some people don't even feel like they need to medically transition, some people switch clinics, some people move countries, some people die. Fourth, it was a limited study of 45 children in one clinic. Fifth, it was 1995 and we're talking about a fast moving area of a fast moving field. Finally, non-binary people would have been counted amongst those questioning their identity because they don't identify as being strictly male or female. Non-binary people may sometimes go through some sort of transition to attain a more androgynous look, but obviously it's not even nearly as common as wanting to transition is for transgender people who still fit into the binary.
(**N.B. Some people seem to get confused into thinking that 'trans' is a third gender. 'Trans' is just an adjective, and 'trans' women and 'trans' men are still binary gendered, as they are still women and men respectively. It is generally accepted that all non-binary people are trans, but the vast majority of trans people are not non-binary. Non-binary people do not define themselves as women or men, though they may define themselves as partially woman or partially man, for example.)
Some people are adamant that letting a child transition in literally any case is a bad thing, maybe that transitioning in general is a bad thing, maybe that transgender people are all just 'wrong' and will therefore come to regret any medical changes made just because they 'should'. If somebody thinks any of this, the previous paragraphs may not mean much to them, and yet there are enough studies that paint transitioning in a positive light that their thinking can be dealt with very quickly. Studies such as this one (1 Hormonal Treatment Reduces Psychobiological Distress in Gender Identity Disorder, Independently of the Attachment Style 2013) show transitioning reducing stress or otherwise generally improving life for transgender people. And what about kids, specifically?
This study (2 Mental Health and Self-Worth in Socially Transitioned Transgender Youth 2016) finds that children allowed to socially transition have a rate of depression similar to that of the general population and only marginally higher anxiety. Compared to transgender children who do not socially transition, who the study notes have both high depression and anxiety, this is a great improvement. It's therefore clear that children being allowed names, pronouns, clothes, etc. that match their gender identities is vital to their protection and development.
And as for medical intervention, this study (3 Young Adult Psychological Outcome After Puberty Suppression and Gender Reassignment 2014) checks up on 55 trans men and women at different milestones in medical transition and finds their mental well-being to be just as good or sometimes even better than the control group. As a sidenote relevant to supporting what was said earlier, their average ages were 13.6 for starting puberty blockers, then 16.7 for starting HRT, and 20.7 for receiving SRS.
I am sure that some people will still say that no transgender kids should be allowed to medically transition just because of the mere possibility that a small minority could regret it. Satisfaction with transition shown above is strong evidence that nearly everyone who actually transitions (again, not just 'visits a clinic') is actually transgender. It can be reasoned that denying transgender children the power to transition based on a tiny minority of potentially confused cisgender (non-trans) children is fundamentally transmisic. It is the idea that a single cis child actively choosing to go through the wrong puberty is somehow worse than a much larger group of transgender children being forced to go through the wrong puberty. It is valuing the lives of cis people above the lives of trans people, rather than treating these two groups as equals.
The reality of the situation is that transgender adults were once transgender kids, and that the longer gender dysphoria goes untreated the more difficult transitioning is going to be for them. Doctors and clinics are doing their best to talk to children and doing their best in general. Drugs and surgery are offered very cautiously and often much more cautiously than patients would like. And the science surrounding transgender issues improves in response to real data while the anti-transgender rhetoric responds only to its own paranoia.