Relatives bring their children to me at family functions to be 'checked'

I work as a special educator. At almost every family function now, someone brings a child over and asks me to see if he is "normal", or to say whether a daughter's reading is behind. Usually within earshot of the child, and often with three other relatives listening. I don't want to be rude to people who are clearly worried. But I can't assess a child in ten minutes between lunch and the gift line, and anything I say casually gets repeated as a verdict. Last month a cousin told her in-laws that I'd "said he was fine", when all I'd said was that he seemed happy. For those who are teachers, doctors or therapists, or who have one in the family, how do you handle this? And parents, what would you want from a relative in my position?