Most kids who think they are trans are not. Many are gay and just don't fit into society's stereotypes. A significant percentage have other underlying issues, such as mental illness and autism.
When they reach adolescence, a time of the proverbial identity crisis, they are especially vulnerable to messages in the media and on the internet.
There are many reported instances of social contagion, just as we see with teen suicide,
The difficulty is that the media is not reporting these troubling trends. And people who speak out are accused of being transphobic. At the same time, there is are many people who now call themselves gender therapists who are only too willing to make money off of this. Just look at all the gender clinics that treat what is supposed to be a very rare condition. They are literally experimenting on children with dangerous hormones and surgery.
You can read more here:
https://youthtranscriticalprofessionals.org/