This is cool stuff! My son is not even two but he loves to watch TV extensively, and I dare not wonder how he would react to video games when he grow up. Here is a gadget that let you control the amount of time that your children spend in front of TV and computer. Simply hook it up, lock it (yes, your kids cannot simply remove it. haha) and give each of your kids their password. The screen will automatically turned off when the time is up.
Check out http://www.usebob.com/