What's "family status"? AFAIK there is no protected "family status". The typical protected classes are race, sex, religion, age, and in some places, sexual orientation.
You shouldn't ask because you can't discriminate "because of marriage to, or association with, an individual of a particular race, religion, national origin, or an individual with a disability" (Title VII).
You don't know if the interviewee is married to a Muslim, an invalid, etc -- if they are, you're open to a lawsuit claiming that was the basis of your discrimination. Just don't ask!
Note that bullet point #7 only seems to apply to housing.
For the second link, it seems like most include protection for marriage status, but almost none for familial status. I'm not sure how that translates in this scenario.
Usually "married with kids" or "are going through a divorce" or "has really sick parents/children they take care of."
Note: It's completely acceptable to discriminate against your boss though. If your boss is going through his fourth divorce and has 8 kids, maybe you don't want to work there.
