(A JAM C) Before I write anything, let me throw this word out...
I am 100% guilty of staring at biracial people. However, when I stare at them, I get an awkward crooked smile on my face... especially when I see little biracial children. It reminds me of my childhood, and almost any memory before the tenth year of my life is a pretty sweet one.
You, however, are probably far more guilty than I. When you see a white woman walking around and holding hands with a medium skin-toned little boy, everything starts to click in your mind. "Hey! She's white... and that's probably her son/daughter... so that means that... the father is black! How did that happen?" And during the 5-10 second period that all of this is going on in your mind, you're looking at the two of them. Let me tell you a little secret. It's obvious! It's obvious to them. It's obvious to the people around you. It's obvious to EVERYBODY... except for you. Somehow, your staring has eluded you, and your mind is so entrenched in the moment that you don't even realize it.
I'm sure that you realize it isn't something we particularly appreciate, but I wanted to bring out the awareness of the issue because it happens too much, and even though I'm guilty too, my guilt is a misdemeanor, while yours is much more severe. It's all good though. Biracial children are beautiful. Stare at their beauty, but just don't make it awkward.