I do think it's important for primary care providers to discuss this with adolescents at office visits, and I agree with the member who said we mostly need to be listening. But if we don't ask we risk not uncovering what may be a source of great anxiety. "Some teenagers have questions about their gender identity/whether their assigned birth sex matches what their brain tells them/[whatever phrase you want to use], and that's perfectly normal as they're trying to figure out their place in the world. Any questions about it that I can answer for you?" (Or, "Does this sound like you or anyone you know?" might work. Teens sometimes like to ask about 'a friend' when they're seeking info for themselves.)
A 12- or 13-yo is not going to be surgically transitioning, but they may take GnRH blockers to delay the onset of puberty while transitioning socially. Hormones come a little later in adolescence. A lot of trans therapy is close monitoring while weighing risks/benefits; hormones aren't risk-free, but neither is forcing a trans adolescent to live in a body that they don't want. (Let me say now: I fully understand that not every trans person wants to surgically transition, and that decision should be respected in either direction.)
There is a high incidence of mental health issues in transpeople, but it's not because they're defective, it's due to shame and stigma. THAT'S wrong.
If a care provider told my kid (trans or otherwise) to honor the body they were given, I would interpret that as them being told that dysphoria's is not legitimate, and that's inappropriate. Trans kids, especially, are so so vulnerable, and they are almost assuredly going to have a lot of adults in their lives telling them what to do. They're going to need a soft place to land. Based on what we know about sex, gender, and development, it's scientifically sound that we be that for them.