SAN FRANCISCO — Stuck figuring out your favorite mobile game app?

Try asking your nearest toddler; she just might know how to help.

More than one-third — 38 percent, to be exact — of children younger than 2 have used a mobile device, up from 11 percent two years ago, according to a national survey being released by the media-monitoring and advocacy group Common Sense Media.

At the same time, young children are spending less time watching TV.

The survey of 1,463 parents found that three-quarters of children ages 0 to 8 had access to mobile devices, both smartphones and Internet-connected devices like tablet computers and iPod Touches. The proportion of young children using the devices nearly doubled, from 38 percent two years ago to 72 percent, and average duration of use tripled from 5 minutes to 15 minutes daily.

The percentage of young children who are using mobile devices every day doubled, from 8 percent to 17 percent.

“This is a really significant shift,” said James Steyer, CEO and founder of Common Sense Media, about both mobile-device use and an unprecedented drop in young kids’ TV viewing. “The data shows rapid and profound changes in the 21st century in both childhood and learning.”

Children up to age 8 spend an average 1 hour and 55 minutes a day in front of video screens, including televisions. That’s on average 21 minutes less than they did two years ago, a significant drop.

Half, or 57 minutes, of screen time is spent watching TV, a drop of 9 minutes a day from two years ago. Of TV time, one-third is spent watching prerecorded programs on a DVR. Ten minutes a day is spent playing video games, down by 4 minutes from two years ago.

Still, one-third of children have televisions in their bedrooms. Lower-income families were more likely to have the television on all the time than higher-income families and those with higher levels of education.