Children are not choosing to live their lives the way they want to, and they cannot consent. It is adults who are inflicting mutilation and sterilization on them. That needs to stop. There are no trans kids. What people do as adults is up to them as long as it does not affect the rights of others. If they say they have changed sex (which is impossible) then they encroach on the sex-based rights of others.
Discussion
I agree that this only applies to adults. Minors should never be allowed to consent, because they are still developing mentally and physically.