This afternoon we were playing outside and our neighbors had some friends over.  We were outside for maybe 5 minutes and the kids were playing with the wagon. The little boy of the friend of the neighbors said that he hated our middle son Jack. Now Jack is a very sensitive kid, and his feelings get hurt very easily, so this really upset him. He came over crying to me and told me what happened. The other little boys mom was standing near me as he came over, she also heard the story and did nothing. So I walked over and asked the little boy if he said that and he said that he had, so I told him that he was not allowed to play on our wagon anymore.  About 10 minutes later, our youngest Will was standing on the grass watching everyone playing and the same little boy ran right into him with a bike causing him to fall and get hurt. I looked at his mother because I thought she should have done something, but she did nothing, so I very obviously told the kids that if the other kids were not going to play nicely we would have to go in the house, and then we did. My question is...what should I have done in this situation? I really don't feel comfortable disciplining other peoples kids, but I also don't think its fair for my kids to have to go in the house because someone else is misbehaving...so what would you have done?