A. You can make your preference known without sounding offensive or demanding. Basically, you're asking other parents to forgo their own customs and take on yours. The most graceful way to do this may be to put the onus on you for being old-fashioned. "I know this may seem like something out of 'Leave It to Beaver,'" you could start off, "but we're teaching Janey and Nick to call adults by their last name, so we're asking other kids to use our last name too." My friend Elaine is so successful at getting children to call her by her surname that even I sometimes think of her as Mrs. Shumway. She has no compunction about saying to a child, very sweetly, "You can call me Mrs. Shumway -- I think that's nicer."
The reason this is a tricky situation is that everybody seems to agree that people have a right to be called the name they prefer, not the name you prefer. But that's among peers, where age-appropriateness isn't a factor. When kids are involved, one parent's preference for more formality trumps another's preference for less because:
a) It's rude not to honor a request for formality, whereas it isn't rude not to honor a request for informality.
b) You don't mess with another parent's child-rearing game plan. Adults who choose to be on a first-name basis with kids are probably doing it out of a desire for casualness more than any ideological mandate, so there's less risk of offending them.
I say this as a mom who doesn't actively enforce the Mr. and Mrs. tradition. I ask kids to call me Trisha unless I know that their parents prefer they use Mr. or Mrs., and then I happily answer to Mrs. Levine (my husband and children's last name but not, legally, mine). When I introduce adults to my children, I use their last name, figuring that if they want to be called by their first, they'll say so.
Trisha Thompson is a contributing editor to PARENTING and a former editor-in-chief of BabyTalk.