As my kids are tempted to stay inside rather than playing and exercising outdoors, I use parental control software and the problem is resolved. My kid has no reason to complain, because we all agreed on how much time he would have on the computer each night.
I don't have to watch the clock, and my son is learning a little something about time management. Kidsemail.org allows me to set different time limits such as hours of the day, daily duration.
It can also block Internet browsers, e-mails, messengers and keep them blocked for as long as you schedule it. I can easily add/remove time on any particular day with just a couple clicks.

You can try it..

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http://www.kidsemail.org/