The grand leap of logic. The problem reported was "white guy in possession of black children". There was no complaint about who the white guy was married to. You have invented a problem that did not exist. The family you saw was a more complete picture ... what you assumed were a father mother and child. I hope your assumption was right and the next time you see that child is not on a missing poster. Of course, if there was nothing else to make you suspicious you're probably OK.