[She briefly glanced over to where he was heading. It was hard to really make out anyone in the mist, since it was rather thick. Other than the occasional shadow that could be made out.]

Calm down for a minute you can't go charging off like that in a place like this. For all we know that might not actually be 'people'.
[Which means the boy will get himself in some serious trouble.]

Can't be reckless in a place like this. There's no telling what's here.