I don't think it is a negative thing at all - at that age it is just innocent curiousity. I think it is great that they are interested in learning about the world around them. But sometimes it can put you in a no-win situation, especially if the person your child is talking about doesn't understand kids or have a sense of humour about them and especially when your child doesn't understand or just ignores any attempts from you to divert the topic or get them to understand that it is innapropriate to speak like that about others.