Per ACGME rules, programs can't ask you about your family. Therefore questions such as "are you married," "Do you have any children," or "are you pregnant" are off limits.
That being said, they still get asked quite frequently. Some of that is because programs are ignorant of the rules, or purposely break them, but I think it happens more commonly due to a truly innocent slip. Hell, if I met someone for the first time and struck up a conversation with them two of those questions would be the first things I'd ask. It's just natural in the flow of small talk between interviews to ask those kinds of questions.
Even with the above knowledge, I wanted every program I interviewed at to be 100% clear that I am married and have kids. I put "spending time with husband and infant son" on my ERAS application. If that makes me not a good fit for a program, I'd rather go elsewhere. If it took me off their list then I consider that saving everybody some time and frustration.
If you wanted to make programs aware but you didn't have something like that on ERAS, don't worry. You'll have opportunities on interview day to make it apparent.
You will get some form of "tell me about yourself" or "what do you do for fun" and just run through a few practice answers where you bring up your family. When you get asked "what questions do you have for me" you could also ask if any current residents have children, are married, are pregnant, took family leave, etc which could be a natural segway into your own personal situation.