Will admit to not having read the preceeding posts to mine. So, with that in mind, this may be repetitive. But.....my older kids' friends always called me Mrs whatever. They are 38 and 35. My youngest, 18, has one or two friends that have always called me Diane. Other adults were appalled, but it was a choice I made, back when these kids were about 3. Her other friends have called me Mrs B right up until last month. Now, there were a few precocious kids that decided it would be cute to call me Diane, so I returned the favor and called them Mr 'whatever' or Ms'whatever'. They got the message very quickly.
Now, they have graduated and I'm sure there are some that I have known forever that will be allowed to be more familiar now that they are 'adults'.
But, my dd has always use Mr, Mrs, etc., when addressing any adult..unless they told her to use their first name (which happened only once or twice). It's a form of respect. But, I'm sure that many of the kids that my dd grew up with will continue to call me MrsB....for a long time!!!