I think the two young girls who attempted to murder another girl in the name of the fictional character slender man were mentally ill and should receive psychiatric treatment until such time as they pose no threat to the public. That may be three years with credit for time served or it may be never. This should be a matter to be determined by competent psychiatrists if any can be found. A twelve-year-old child with a clear mental illness can’t be held totally responsible for their actions in the same way that an adult criminal can be held responsible. Punishment should not be the objective and safety of the public in the future should be the overriding concern.
Access to material such as slender man should be restricted by law to legal adults just like alcohol, cigarettes and pornography. There is a lot of garbage in the world and the people who shovel it on the heads of children should have some type of legal restrictions placed on them with severe criminal and financial penalties for violations. Even adults are not always capable of controlling their actions when they fill their mind with negative images. Children should be restricted from accessing many more types of negative material by their parents and the government. The internet makes restrictions difficult but not impossible. People producing these types of materials could be taxed and the money used to police the illegal distribution of this crap.