Unless it's consistent and the same child doing it, there isn't much you can do. Toddlers do this all the time.
My DS was bitten a few times by the same child over a period of a couple of weeks. I eventually threatened to lodge a complaint when I heard the parents weren't concerned and said it was the nursery's problem . Needless to say that particular child was watched like a hawk and it never happened again.
I worked in a nursey for almost 4 years and spent most of the time working with toddlers aged 2 - 3 years. Biting is most common in children this age and i can assure you when it happened in my room (i was suppervisor) it was taking very seriously. child who was bit was comforted and child who had bit was taken away and spoken to about it. accident and inccident forms were filled out for both parents with 1 copy going home with them and 1 copy kept on file. parents were spoken to at the end of the night. most of the time, parents did understand that it was just 'one of these things' and most of the time it can just be a one off.
we did have a child though who seemed to bite rather alot. he struggled with his speech and would bite when he was frustrated. His parents were very concerened but it seemed to pass after a few months.