I've always been a listening ear for people, especially young people who might feel they can't talk to their parents for whatever reason. I've always told them they can tell or ask me anything and I would help them and that I would not tell their parents unless I felt they were in danger, either from themselves or others. Obviously I always encourage them to talk to their parents or, if they wouldn't, put them in touch with a Dr or other agency.
If your teenage son/daughter was feeling anxious and depressed but didn’t feel they could talk to you about it and went to a family friend in confidence instead how would you feel? And what would you think of the friend if they did that? Would you be angry and think they should have told you?
I would be sad if my boys felt they couldn't come to me but really grateful they trusted someone else enough to go to. And that my friend was good enough to help. Telling someone is always better than the alternative isn't it?