Anyway, there are already a few boys at daycare who are very cliquey and bully my son, so I don't see why I shouldn't try and protect him.
Edit: I also see a big difference between hitting and biting. I know kids don't see the difference but I wouldn't tell my child not to play with someone if they just hit him. In fact, I never tell my child who to play with and I wouldn't, I haven't in this situation.
By 'avoid them' I mean I wouldn't be encouraging the friendship, like i wouldn't go and seek out the mum of this child for a play date, unless my son specifically asked to play with him. Basically what I'm trying to explain is that I haven't said anything to him either way about this child as I don't even know him, all I said so far was that it wasn't nice of him to bite him and that if he does it again (or anyone else for that matter) then he must tell me or his teacher. I just won't be organising play dates with this child unless my son asked. (For the record, I haven't organised any playdates for him with any of the kids anyway as I don't actually know who his friends are or if he even has any, except for one boy who he played with a few weeks ago and DH happens to know this boy's father so we were going to arrange it)