According to Wikipedia, 6 7 apparently stands for Gen Alpha or its meme culture, like an insider joke that secretly refers to Generation α. It even got an avatar called mason representing a stereotypical white alpha boy. (Correct me, if I am wrong.)
im sorry but the 6 7 kid shouldnt d!e for what he did. ki\\ing a kid who has their whole future ahead of him isnt enough to justify like 5-8 kids screaming 6 7 every 2 secs