Kids, even teenagers, have little concept about the depth of what they're doing. To them, they're truly "not hurting anything" and don't think about it.

We have a teen son and I had to have that discussion with him a couple of years ago. He and some pals were just chilling out in the woods and I asked if he knew who's woods ... "No, but we weren't doing anything wrong" ... thus, the conversation with him and point made about trespassing, upset landowners, potential danger during deer season, law enforcement, etc.

Problem arises when the parents don't care and won't back up your request to cease. Then they get all pissy if law enforcement is called in. But that's what you have to do sometimes.