Actually kids aren't stupid these days they know death is permanent and on some level understand the finality of death. Even kindergarteners can tell you that much.  

It's not unusual for a kid to want someone to die so they don't get picked on or bugged anymore but it's not common for them to come up with a plot and take steps to inact a poisoning plot. This situation is fairly unique by those standards.  That's the only reason it's made media notice.