SAN FRANCISCO — The people who are closest to a thing are often the most wary of it. Technologists know how phones really work, and many have decided they don’t want their own children anywhere near them.

A wariness that has been slowly brewing is turning into a regionwide consensus: The benefits of screens as a learning tool are overblown, and the risks for addiction and stunting development seem high. The debate in Silicon Valley now is about how much exposure to phones is O.K.

“Doing no screen time is almost easier than doing a little,” said Kristin Stecher, a former social computing researcher married to a Facebook engineer. “If my kids do get it at all, they just want it more.”

Ms. Stecher, 37, and her husband, Rushabh Doshi, researched screen time and came to a simple conclusion: they wanted almost none of it in their house. Their daughters, ages 5 and 3, have no screen time “budget,” no regular hours they are allowed to be on screens. The only time a screen can be used is during the travel portion of a long car ride (the four-hour drive to Tahoe counts) or during a plane trip.