I've heard about the mewing trend too, and from what I understand, it's related to a YouTube personality named Mike Mew who talks about orthotropics, which is a method of improving posture and facial structure. Apparently, some kids are trying to apply these principles to change their appearance, like their jawline or facial shape. It seems to be more of a fascination with self-improvement and aesthetics rather than anything harmful, but as a parent, it's always a good idea to have a conversation with your child about why they're interested in it and make sure they're not taking any extreme measures.