[~Misguided Ghosts~]

I don't think it would hurt to tell their parents. Don't think of it as getting them in trouble, but think of it as a concerned parent talking to another parent. I think letting them know gives them the opportunity to talk to their children and see what they're up to, and make sure they know they're loved. If they are addicted to these substances as well, it could be the first step towards them getting the help they need.