I work very regularly with schools where weapons are brought by children in elementary school. It is unfortunately more common than we would like it to be. Children regularly spend time unsupervised at home, looking for objects of interest. It is unfortunate that they often can find guns and drugs. This crime that we witnessed was a crime in part because of the weapons that were available.
Children often get into disagreements in elementary school.
That's nothing new. What is new is that they often don't have the skills they need to have learned from adults to resolve these problems, and they have the means to make the consequences more dire and deadly. There are many causes for the violence we see. Because there is no one cause, there is no one group or behavior to blame. We all share in the responsibility.