Help please with PC monitoring issue?

I have installed Advance Parental Control on my family PC's as one of my children has been accessing sites. He is very good on computers however and has deleted the program files for the program thus stopping it from working. I have re-installed the program and have found that you can simply delete the programs folder / files simply by finding the folder and pressing the delete key. I have tried locking the folder from the group policy but because it holds a running program that starts up with the PC as soon as I restart the PC the folder permissionss seem to be over-written and the folder is open to do anything with it again. I have also tried the freeware software 'My Lockbox' but again because the program starts up with windows xp the folder is available. Any ideas would be appreciated. PS: I thought of pwording my account and limiting all other accounts but he has shown me before how he gets past user login pwords.