I don't allow it. Kids act differently with others here and I feel uncomfortable being watched. I have only ever had 1 family ask. I said no. The kids were here just a few weeks, one kid went home with a scratch from another child on his neck and they gave their notice. That's just too overprotective for group care IMO.
If a family wants to just leave child for a few hours a few days at the beginning that's fine (while paying full rate) but no they cannot stay.