Su Hijo?

Our family status has been questioned in Mexico much more than at home. We hear the question "Su hijo?" a lot. I guess it's because people here recognize E as Mexican, and me especially as "guera." At home, I think people are more likely to ascribe our race to E, not looking closely. I don't really know because we have almost never been asked to explain our relationship to him. In four years, I can think of only once. I'd say it happens twice a week here. Intellectually, I know all this, but it's still jarring when you're explaining you adopted your son to the clown making him a balloon animal for 5 pesos at the mercado.