Sister Golden Hair Surprise

So last tuesday Scott and I were called upon to babysit the kids of Scott's boss, Jeff, while he and his wife went out of town. I thought we would go in the evening and have a nice time, but really I had to go around noon and tend the kindergarten age boy, Nathan, by myself while scott was at work. He and I hung out all afternoon, talking and watching Pokemon videos, and generally having a nice time.
At 4:15 stan started to fuss, so I went in the kitchen to feed him (carrots and peas, not a big hit, it turns out). About 5 minutes later Nahan starts scraming and comes into the kitchen dripping blood the whole way. I had him spit the blood out into the sink while I called Scott (scott had the car, and although i had the keys to nathan's mom's car, it didn't have a carseat for stan). In the process he spit out half a tooth. I was cleaning that up when I saw the long cut under his chin. It was probably an inch and a half long, but on his six year old chin it was almost from side to side. It was bloody, but not dripping or anything. I had him show me where the bandaids were, and i took him into the bathroom to clean it up. I couldnt' really tell how deep it was, but by the time scott got there the edges had kind of spread apart and I knew he would have to get stitches. The older boy was about to get home, so I stayed home with stan to recieve him while Scott took Nathan to the neighbor, who is a dermatologist, to get stitches (at the suggestion of Nathan's parents). The cut was so deep that he had to get three layers of stitches; Scott said it was all the way down to the bone. He was in pain, but when we gave him childrens tylenol he seemed to be fine, so I thought everything was taken care of.
In the morning he got up and dressed just fine, and he didn't really complain untill I accidentally mentioned the possibility of not going to school. Karen came and took over for me, but i went over to her house for the day. Nathan was feeling pretty tender, but again, when we gave him a regular dose of children's tylenol he was talking and playing and seemed just fine. In the afternoon, his face started to swell a little, and Karen suggested that he may have dislocated his jaw. But at that point his dad was going to be home in two hours, so we decided to wait for him and he could take Nathan in and have it looked at. By the time I left Karen's house, his face was getting fairly round. Well the next day scott came home to report that his jaw was broken, that he had some surgery on it, and that it would be wired shut for two weeks. I had no idea! I feel terrible about the whole thing.