D.R.
I was also taught to address adults by "Mr./Mrs. (last name)," "Mr./Ms. (first name)" or "Uncle/Aunt (first name)." I have also tried to teach my children what is the most respectful way to address an adult. There have been a few times when a child has just called me by my first name, but I, very nicely, correct them and tell them that I prefer to be called Ms. (First name). Most of the time, I don't have to correct them again, but there are others that just don't seem to get it. Politely correcting them usually does the trick, even if its every time you see them.
Good luck!
D.
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