Greg,
You've brought up some very good points. Yes, if this has been an isolated incident then talking to the guy might be as far as it needs to go. But I think I would still want to arrange for a new person to do the cleaning. One point that doesn't seem to have been brought up. Is this person really the only one with access to the property? Or does this fellow have kids of his own and had to bring his child with him for some reason? If he'd needed to bring his child for lack of childcare and the kid got into things without his parents knowledge.... Not terribly likely but not impossible. I'd still change the locks, though.