I understand that the parents had booked the rooms, paid for them, and were settled in. . BUT had I been the one there with my kids I would have went somewhere else asked for a refund later.
I'm sure it would have been impossible to find another hotel on such short notice so thats when you use your brain. You cover your kids eyes, take them straight to the room and make them stay in there! Not to hard huh.
Maybe the group of swingers didn't inform the hotel that they were going to be boinking eachother all night.