I haven't really thought much about it--but I just figured out why my kids (50 & 52) called some adults/parents by their first names and others Mr./Mrs. If the "parents" were family friends and we all called each other by first names, so did the kids. If my kids met parents through their kid-friends, they automatically called them Mr./Mrs. unless they were told otherwise by those people. They generally wouldn't have known their first names. If an adult was introduced as First Name, they probably used it. In any case, they had BETTER have been respectful.