Older DS aged 16 just returned from a trip by long distance bus and ferry to visit my parents with younger DD aged 4. He was a bit shocked because several people had assumed that he was his sister's father. This happens to older DD aged 19 a lot (someone assuming she is the mother of her sister) and she really hates it. You have to be careful with teenagers but generally I don't think there is anything rude about assuming that an adult who is with a child is that child's parent. That may not be a case but it can be difficult to completely avoid any assumptions. Asking doesn't necessarily help in my opinion. If someone is offended by an assumption they will most likely also be offended if you ask. It's the mere thought that counts. At least I know DD was offended when she - then aged 15 - was waiting for DH in a doctor's waiting room and the doctor came out and asked if she was his wife.
The difficulty also occurs if you don't know if two people are a couple or maybe father and daughter. If you have to make a guess or ask I think it is better to assume or ask if they are a couple. If you are wrong you have most likely only offended the daughter. If you make the assumption the other way around you will offend both if you are wrong.
I suppose the etiquette correct thing is to never assume anything about the rel@tionships of others but it can be a bit difficult in real life. When do you think an assumption or a question about a rel@tionship is rude? An example of an assumption or question I find rude and strange but have been met with several times is that because of the age difference between my children now 19, 16, 12 and 4, the youngest must have a different father than her siblings. This is not the case but is probably in part caused by the fact that DH looks much younger than me (he isn't)
When you say "Asking doesn't necessarily help," what kind of question did you have in mind? I think the doctor in your example could have very easily avoided that issue--he could either have asked your DH who had accompanied him (and gotten the answer "my daughter") before going out to the waiting room, or he could have phrased his question to your daughter in a manner with fewer assumptions: e.g. "Hi, are you here with Mr. Mom2four?" "Yes, I'm his daughter, [name]" or, if she didn't volunteer the relationship
, he could ask "What is your relationship
to Mr. Mom2four?" or even "Are you a relative?".
As far as assuming two people are a couple, how often are you in a situation where you need to make this assumption? There are a lot of reasons for two people to be out and about together besides being either a couple or parent and child. In addition to those possibilities, the two people could be friends, co-workers, roommates/housemates, siblings, other blood relations (e.g. cousins, uncle and niece...), etc. If you know one of the "couple", then let them introduce you to the other and you'll likely find out the relationship
without making assumptions; if they don't volunteer the information, then do you really need to know (or assume)? If you have to assume something, then I'd assume that they are either friends or non-specified relatives until you are told otherwise.
The "couple" assumption really gets to me. While I don't recall ever being mistaken for anyone's parent or daughter, I do hang out with my older brother a good bit (similar interests and get along well), and more than one person has assumed that he was either my boyfriend or my fiance--trust me, both of us were quite wierded out by that assumption. (Clarification: A friend asking me, "So who was that guy
you were with at the festival?", obviously guessing romantic interest, surprised me but was very funny; the guy who had just met both of us on a group trip asking "Oh, so this is your fiance?", obviously confident that we were romantic partners of some sort, was both shocking and kind of creepy.
) And if someone assumed I was my father's wife, I wouldn't be the only one offended; I really doubt my dad would appreciate either of the possible implications--that his "little girl" looks twice her age, or that he, a middle-aged man, would be married to a girl barely out of college (even if "cradle-robber" implications wouldn't bother him, the fact that the girl in question was his "little girl" would