Return of the biter

So Henry's got an amazing daycare provider and 4 of the 5 kids that go to her are wonderful. Henry even has a girlfriend at the sitter, however, there is one monster who won't leave my baby alone. Since he's been going to the sitter, he's gotten bit 6 or 7 times by the same child. I have tried talking to the provider, she assured me the mother has been notified and is working with the child. That was 2 months ago. In the last week, Henry's gotten bite three more times. TWICE IN ONE DAY! WHAT DO I DO??? I am at my wits end. I had to discover the last 3 bites myself. The latest were last night while I was giving my baby bubba a bath. Two very distinct sets of bite marks on the same arm. HELP ME!!!!!!!! ANY ADVICE??