Welcome to Susan's, hugs
I started when my daughter was 14 1/2. She is turning 17 next month. My wife outed me in June in a very awkward way. My daughter had a week where things wee tense but now things are good, as long as I do not express, that will come in time.
6 is young and they are very resilient. Jennifer Boylan has 13 books, one of which was about raising her 2 children. I would seek out a gender therapist that deals with adolescents. That person would have a lot of experience dealing with this issue.