Kids see unacceptable things happening around them all the time, and in their own direct and innocent way, point them out to us as adults. Often our own feelings of guilt cause us to rationalize what the child is observing and commenting on.
Let's take a specific example. You stop at a traffic light and a beggar comes to your window. You decline to engage with the person who is asking for food or money. Your child observes this and asks why this person has to beg and why you did not help them. Your mind is elsewhere and you trot out a standard rationalization. The beggar happens to be a black person and you have inadvertently reinforced that it is okay to view black people as less deserving of respect and compassion. You have missed an opportunity to sensitively chat with your child about a situation that is unjust and to engage in a discussion that does not rationalize the status quo in any way.
It is a scary fact that experiments have shown that normal, well adjusted people can be persuaded to hurt and even torture others, as long as they are provided with plausible rationale.
Remind yourself of an experiment that many of you will have heard of, involving students from a prestigious American university: A group of students were convinced that they were participating in a learning experiment, which required them to administer painful electric shocks to the subject of the experiment.It was a fake experiment and the subject was an actor who pretended to experience pain when the participants pressed the button "that administered the shock". The students were urged on by a plausible, authority figure wearing a white laboratory coat and they compliantly administered shocks to the screaming "victim". Shockingly, well over half the students continued to administer the shocks even after the victim apparently passed out. The experiment demonstrates that even intelligent, decent people, when exposed to social pressure from a plausible authority figure, will ignore their sense of morality. This provides insight into the many atrocities human beings have committed and continue to commit.
My point is that you are a plausible authority figure to children and you need to use this authority responsibly to talk to them about rationalizations that people make about doing things that are morally wrong and to challenge such.