How many times have you said (okay, yelled) something along these lines? How many days of the holidays are left? Perhaps it is time to sit down and make a plan. Read this eminently sensible article, by Larry Magid and consider a Family Contract for Online Safety and Smart Use of Technology
Do it together. Build in some discussion. Remember it’s the holidays. Cover all devices. Make some compromises. Be fair and reasonable but in the end agree to disagree! Finally, have some rewards ready for meeting the contract and some consequences for not following the rules.