The Microsoft founder said his 10-year-old daughter, his oldest child, was not a hard-core Internet and computer user until this year, when she started at a school where the students use tablet computers for almost everything.
"She became very avid and discovered a lot of computer games, including one that runs on the Xbox 360 called Viva Pinata, where you take care of your garden," he told a business audience in Ottawa.
"She could spend two or three hours a day on this Viva Pinata, because it's kind of engaging and fun."
Gates said he and his wife Melinda decided to set a limit of 45 minutes a day of total screen time for games and an hour a day on weekends, plus what time she needs for homework.
Microsoft's newto control the Web sites their children go to but also includes an audit log that records sites they have visited and whom they've been instant messaging.
"Up to some age, to be determined, it's very appropriate for a parent to get a sense of what they're seeing out there and be able to have conversations about it," he said.
"My son said, 'Am I going to have limits like this my whole life?', and I said, 'No, when you move away you can set your own screen limits,'" Gates recounted, to audience laughter.