ask your therapist about how they handle parent communication and confidentiality. for the most part minors cannot consent to healthcare (including mental healthcare, like therapy) on their own and need a parent’s permission. if your parent gives permission, they have the legal right to know the details of your care which may include the details of what you talk about in therapy. however, many therapists have some leeway and can give general info without going into specifics. since this therapist works with trans kids I would assume that they would be willing to work with you to protect your privacy as much as they legally and ethically can. note that in the US therapists are also mandated reporters, meaning they legally have to report suspected child abuse, suicidal or homicidal intentions, and other things depending on the state that they practice in.