I this true (children and animals can sense when a person is shady)???

My father always said that children and animals can sense when a person is up to no good.My father had a dog that never cared for a neighbor. He would bark like crazy when the guy entered the yard. My father found out the guy was stealing from him. My son has never wanted to be around my sister. He has never been alone with her. Whenever she comes for a visit he will run away. When he was a baby he would scream to high heaven if she even glanced his way. I know my sister has been very shady since a child. She does mean things to people at times and thinks it's funny. My son is now 4 and he simply can't stand to look at my sister. I first thought he was this way because he wasn't around other people other than his siblings.He is now in school and is around other kids. He will conversate with other people in the family. Even when we're out and about he will say hello to people when we pass them. He is otherwise a friendly child. Do you think it's just a phase? Or do you think that old saying has some truth to it?