My mind, on reading "are they yours" goes directly to the 'adoption' question--which would leave me peeved.
Because my child is my child, whether I gave birth to her, adopted her, or she spran fully formed from my head.
I think, as someone said above, the complexity of racial relations makes it a more volatile question than people realize.
(and, when talking to kids, I know the situation can get squirmy awfully fast--step parents, mom's or dad's boyfriend, foster care, grandparents who are guardians, etc. So when I deal w/ kids, and I need them to point me out their parent, I just ask who their 'grown-up' is. Saves some aggravation and "uh, that's Cindy, she's the nanny" embarrassment that kids sometimes have)