You are looking after this 4 year old boy under the payment of his parents. I'm all for telling the parents privately as to not embarrass him, but the parents have a right to know if he has an accident in his pants so they can parent him the way they see fit whether we like their way or not. We do not know what goes on at home, it may be a sign that he has a stomach bug of some sort, but the parents should certainly know, no question about it. They don't need to know about every time out or correction they receive throughout the day, but a potty trained older child having a bm accident is necessary information in my opinion. I'd be ticked if you didn't tell me because my child asked you not to. As a daycare provider I would have done what you did and discretely told the parents and told them he was nervous about telling them. It would not have even been a question in my mind about WHETHER I should tell them.