What actions could I take to protect myself in regards to bad behavior from a child under my daily care ?

I have worked for an organization for 16 yrs. which specializes in the care of school age children. I have never had a mark against me for any misconduct on my part in all that time. I basically follow our policies on dicipline which entail sitting out or privileges revoked when needed. If a child misbehaves we are also for the most part supposed to right up a report discribing the incident which is then to be signed by the parent. I feel that this one policy is sometimes abused- I feel that children are going to misbehave or not follow the rules from time to time so I don't usually write them up for every little thing they do unless it is something serious. I have two brothers under my care who come from a family with many dysfunctional issues going on in their home & they both have a tendency to bring these problems into the program by hitting other children when they don't like something, talking back to me, & basically defying me every chance they get which has become quite disruptive in the everyday functioning of the program. I have spoken to their mother on certain occasions & she usually speaks to them about their bad behavior in front of me & makes them opologize to me but, the next day they are back at it again. The final straw happened yesterday when the older child did not like the fact that I made his brother sit out & decided without my knowledge to call his mother on his cell phone & tell her that he was scared because I had put my hands around his brothers neck & was choking him. When she came to me & acused me of this I was, to say the least, flabbergasted. I told her that never have I laid a hand on any child & once her son was questioned he retracted what he had said & then was told once again to apologize to me. Now, today he is misbehaving once again but, now I feel that my job is in jeopardy because of what he might tell his parents. He can sence that I feel this way so he now thinks he can get away with anything he wants because he will call her with some made up story again. I did go to my superior about this but, she was not much help to me in dissolving this problem I am now faced with. I would appreciate any insight from someone who might of been in the same predicament before or any suggestions on what I might do to remedy this on my own. I would hate to have to throw away that many years because of two young boys who think they have one up on me. Help!