YANBU. The ratings are a LEGAL guideline - the parents are committing the offence of neglect if they allow their children to watch them, as they would be with porn or horror.
Try checking out with someone in school that understands about child protection. Here is the definition of neglect -
The government guidance for England, Working together to safeguard children (HM Government, 2010), defines neglect as:
"?the persistent failure to meet a child's basic physical and/or psychological needs, likely to result in the serious impairment of the child's health or development. Neglect may occur during pregnancy as a result of maternal substance abuse. Once a child is born, neglect may involve a parent or carer failing to provide adequate food, clothing and shelter (including exclusion from home or abandonment); protect a child from physical and emotional harm or danger; ensure adequate supervision (including the use of inadequate care-givers); or ensure access to appropriate medical care or treatment. It may also include neglect of, or unresponsiveness to, a child's basic emotional needs."
The PEGI 18 rating :
^PEGI 18
The adult classification is applied when the level of violence reaches a stage where it becomes a depiction of gross violence and/or includes elements of specific types of violence. Gross violence is the most difficult to define since it can be very subjective in many cases, but in general terms it can be classed as the depictions of violence that would make the viewer feel a sense of revulsion.
Descriptors shown on the back of the packaging indicate the main reasons why a game has received a particular age rating. There are eight such descriptors: violence, bad language, fear, drugs, sexual, discrimination, gambling and online gameplay with other people.^
Putting it in black and white might help.