My grandmother used to say that small children were the best judges of character, and I've got to admit, I've seen that myself.
I think we all have an intuitive sense, but we are taught at an early age, and rightly so, "don't judge a book by its cover." Although this is so very true, it also makes us not listen to that first instinct quite so much. I think it is important, especially in the times we live in, to stress to kids that yes, we all need to look beyond superficial things in a person, but if they get the sense something about that person makes them uncomfortable to trust that intuitive instinct!