Principal refuses to update me on bullying issue

I am butting head's with my nephew's principal.  He has been bullied by the same two students since the beginning of the school year.  We have repeatedly had conferences with the teacher, updated her on a near daily basis about the situation, and she has always told us she had a conference with the parents.  My nephew is only 4 years old.  Yesterday was our last straw.  It escalated to where he got kicked in the stomach, pinched, and spit on by two different kids.  He has NEVER physically retaliated.  We always tell him to just tell an adult and alert us after school.  (The reason I am so involved is I help raise my nephew.  My sister lives with me, works full time, and since I work from home, I am more able to go to meetings, award ceremonies, pick them up afterschool, etc.)   I had just about had it.  We have had parent/teacher conferences, and my nephew says the teacher puts the students who pick on him in time out, but at some point, she has to realize that "time outs" are not working.  My boyfriend is also a teacher, and my mistake was allowing that association to filter in how patient I've been with this teacher.  I have now come to realize that they are two completely different teachers.   

This teacher has an aide.  I know from firsthand experience keeping up with 20 kids 24/7 is impossible, but when you are aware of a bullying situation, and there are two teachers in the classroom, there is no reason why it should have gotten to the point where it has.

I waited afterschool to speak with the principal and the teacher, and when I asked if the situation had even been brought to the principal's attention, the principal refused to tell me.  She said it was because of confidentiality laws.  ???  I was not asking for specifics of what was discussed, if other students were targets of these kids misbehavior, if other parents had come in to complain - I just requested confirmation that the situation - solely concerning my nephew - had even been brought to the principal's attention.  It sounds ridiculous that she can't confirm that.  Is that really a law?  I have looked everywhere online and cannot find anything that details whether it is or isn't.  I don't even know if I'm looking in the right places.  I have a meeting tomorrow with the principal, teacher, my sister (my nephew's mother) tomorrow.  I hope I can get more insight about whether or not the principal can really refuse to produce such simple information.  How can a parent ever confirm that steps are really being taken to remedy serious situations as bullying if they can never confirm anything they are doing about it due to confidentiality laws???  It sounded like she was just trying to cover her teacher's (and her own) back. 

And, as luck would have it, I found out after our brief meeting that the principal is the grandmother to one of the kids bullying my nephew.  They have no assistant principal.  What step should I take - am I legally allowed to take - to assure that her bias for her grandchild does not discourage the proper course of action?

PLEASE HELP ME!  I am so bothered by this that I have written a letter to request I accompany my nephew everyday at school.  I know everyone thinks this of their kid (I love him as if he were my own), but he really is a great kid.  On the days he tells me what these kids did to hurt him, he will still turn around and wave goodbye to them when I'm picking him up.  The one thing that has always stuck with him is something I used to always tell him when he first started school 2 years ago:  just because a kid is mean to you does not mean you have to be mean to them back.  I've always told him and his brother they are better than that.  You are just not meant to be friends with certain kids.  It's not a big deal.  It doesn't mean you have to say mean things to the kids who are mean to you.  It doesn't mean you have to do anything to them at all.  Just stick to your manners, stick with your friends, and if they bother you, alert an adult and trust they will take care of it.  I am tired of thinking of him at that school, wondering what they're doing to him now.  I would appreciate ANY advice anyone can offer me.  

Thanks,

Janie