Being somone who hopes NEVER to have kids of their own, what I am about to say is based entirely on what I observed growing up. In the last ten years or so there has developed a sense amongst so many parents that because a child is their child the child is incapable of doing wrong. This happens for two reasons, the first being that the parents are so damn egotistical that any wrongdoing on the part of the child - who is viewed almost as an axtention of the parents on body/soul/consciousness/whatever - that does not directly impact on the parent ( cutting up mommy's best cocktail-dress and such) is ignored because the parents take it as a personal insult to them that somone could accuse their child of anything untoward. It's a product of the "Keeping up with the Joneses" "My child's on the honor-roll and yours isn't" society where children are treated almost like medals.

The second is that it is so much easier to blames the schools or the cops or whatever other authority figure brings up the mewling brat's misdeeds than to admit the child has done something wrong, think of an appropriate punnishment and carry it out, that many parents just don't bother. They kid themselves in to thinking the world is singling little Joey Bloggs out and that they should not be concerned with it and just go back to watching TV or thinking about their stock portfolio or whatever.

Both approaches are a lot more common than people realize and are what is really to blame for incidents like this.