Give them a free pass on this one. That being said. You need to lay down the rules from here
on . ? how old are these young ones.

When ours were younger, they had a lot of sleep overs. Some times on short notice--no problem.
Some times the one staying over was really seeking a place to be. Not much home life for some
of those who invited themselves, more or less, to spend the night. They were always welcome here.
You tend to get a clue, when they need to call a parent in the evening, and the call
they make is to the bar. Sad thing is they have the number memorized.
Sure is neat to bump into these young adults every once and a while now,
you get a smile and some times a hug. Never really know how you may have impacted them.
I Keep that old saying in the back of my head.

It takes a village.