Kids getting hurt at preschool

We have a child at a co-op preschool that has a new director.  There are two kids with really extreme behavior issues (throwing chair and large toys and hitting other kids repeatedly including in the head) many times in 3 hour morning.  Parents have said it was same thing last year, which we wish we’d known. 

The two kid’s parents know what’s happening and a lot of the other parents have talked to the director but she’s won’t ask the families to leave.  Our child likes their friends at the school and we don’t want them to have to change since they haven't done anything wrong.  We also don’t want them to get hurt and think that this is normal behavior. 

Any suggestions?