I agree with 2CM.
Check to se that the staff are actually shadowing( following and interacting positively, redirecting any trigger behavior) the child who is biting. They should also be documenting what's happening before and after the incident, what time, day of the week and any other circumstances relevant to the incidents to see if there is a pattern or a trigger to the biting.
Is the other child teething? Do they need something else to bite on?
Did they explain why they can't tell you who the child that's biting is?