In FP-land, there is a magic age between 13-21 where the parent accompanies the minor/adult-child to a wellness visit and says to the minor/adult-child "would you like me to leave so you can talk to Dr. Lauer alone?" Or the minor comes in for the first time for a sinus infection unaccompanied by the parent and has driven themselves to our office with a newly acquired driver's license.
I take these opportunities to say, "you (the minor) are growing up and will have personal and confidential things you need to share with me. While it's best to be open with your parents, there are some things that need to be discussed in private. I add that parents have a legal right as the parent of said minor to see their medical record." And I look at the parent to say "but we discourage this practice b/c it undermines the confidential and trusting nature of the doctor-patient relationship." The parent always nods their head in agreement. Then I say to the minor "if you have serious things to say, I hope you can trust your parents to listen and help rather than get mad." Then I look at the parents and say "Right?" And go on to say "But if you ever need to share things with me, I promise not to disclose this information with your parents unless you have agreed to let me share it. I look at the parents for the confirmatory head-nod.
We have not had the experience where a parent demands the minor's chart to search for confidential information. I hope we never do.