From an objective viewpoint, the adults’ definition probably is better than a child’s but the child’s subjective view is what’s going to affect her (or his) behaviour. If I had been given a punishment that I thought was unfairly harsher than that given to my “partner in crime”, I would have strongly resented that and reacted accordingly. That some research showed my punishment was, theoretically, more lenient wouldn’t cut any ice. At he very best you might, just, manage to persuade me that you didn’t intend to treat me unfairly but, by then, most of the damage will already have been done.