For a start off, I'd be asking the cm what they were about this. How is she they tackling it?
(dd bit another child at the cm for the first time last week. The whole place dramatically ground to a halt until dd apologised, cm raised it with me, explained her plan if it happened again, discussed what we thought I could do at home to re-inforce her approach. i think she dealt with it well. And hope the other child's mother agrees Very different to your situation, but cm dealt with it strongly I felt.)