Times have changed I guess.
If my mother ever heard me call an adult by their first name and not Mr, Mrs, or Miss my mouth would be washed out with soap. There were a couple of Scout leaders that insisted that we call them by their first names. That never sat well with my parents. My observation was those were fun people.
When SWMBO and I moved into the current neighborhood we insisted that the neighborhood kids call us by our first names. A parent objected and got in my face about it. I told her that I would call her by what ever name she desired but "My name is Rich and my father's name was Mister". She was exceptionally irritated, we never really got along before or after that but she moved in less than a year so it didn't matter.
In the 10 years before I retired and shortly after retirement I took a few college classes. On the first day of class the Prof always asks, "Any Questions?" I would always ask, "What do you want us to call you?" All answered to call them by their first name. There was one exception and he added, "For every time you call me Mr. or Prof, I will lower your grade by one letter." Point made.
I think that when the kids call the adults by their first names it creates a level of equality and trust. Both SWMBO and I have had neighborhood kids come to us with some very serious issues. The worst was an underage, unlicensed but a designated driver in a car crash that she was driving. In both cases it was talk to your parents, they aren't going to kill you. In both cases the parents came by later and thanked us for sending their kid in the right direction.
Even with relatives, by the time their kids are in fifth or sixth year we try to avoid the "A" and "U" words.
Is what SWMBO and I do, correct for everyone? Of course not! But everyone has to do what they are comfortable with.