superlizard said..
The bigger concern is, that the parents of those kids don't care what sort of house/family their kids just visited (no direct reference to you Harrow - just talking in general). Whenever i let my kids visit friends, i first take initiative to meet the parents and suss them out before i let my kids go to someone's house. There is too many weirdos living on this planet unfortunatelly. The least i can do is meet the family and work out if they are normal people before letting my kids into their house.
A few years ago one of my sons had a friend from school visit our house, he asked if said friend could sleep over... Sure, no problem...
The friend slept over a few times and got into a routine of coming direct from school on friday with my son, staying the entire weekend and returning to school on Monday with my son. I guess he stayed probably 20 weekends over a year or so. For the entire time, not once did his parents make any contact at all.
He always said his parents were ok with him staying and his behaviour was generally ok. I found it odd that his parents seemed to take zero interest in checking out the people their son was with...