It may be hard for folks outside of the U.S. and Canada to understand the reaction. The plain truth is that Columbine wasn't the only tragedy that has taken place in U.S. schools. There have been multiple shootings, stabbings, extreme fights/beatings etc. Enough so that this at least needed to be looked into. Lets add the fact that the U.S. has become a very litigous society and the police and school boards have been sued for "not doing enough". There also doesn't seem to be alot to explain the Grandparents behavior. Perhaps this child fits some of the other psychological factors found in many of the previous antagonists (single parent, no parent, depression, etc.).
Fiction isn't illegal by a long shot. Some children just seem to know better than to write stories that might get too much attention.