There should be a firm limit set about behaving in any unsafe way. Children should receive a time out if any unsafe behavior occurs, and they should then (at the conclusion of the time out) be made to play alone for a bit before rejoining the other children. Also, it would be very sensible, even though the children are very young, if parents picked up on the behavior and backed up the discipline of the daycare provider. Talk alone with such young children is pointless - actions speak louder than words. Be sure to inquire about the circumstances under which the biting occurs, and why it is that your son is the only victim. It is the obligation of the provider to protect the children from harm, and the fact that this has occurred repeatedly would make me wonder about the level of supervision. You might want to consider changing the daycare arrangement if the situation doesn't change.