More than half (53 percent) of mobile device users reported that they spent more time playing on these devices this year compared to last year. The boost is most pronounced among children 12-17, who were found to spend an average of seven hours per week on mobile devices compared to five hours per week in 2011.

"Kids are engaged with mobile devices as less expensive tablets and an increasing amount of hand-me-down phones create greater accessibility to these platforms than before," NPD Group analyst Liam Callahan said in a statement.

Though desktop computers, laptops, and consoles remain the top devices for gaming, "almost" as many children are playing on mobile devices as they are on consoles and computers, according to the study. In addition, it found that children are starting to play games on mobile devices at a younger age than in prior years (age 8 in 2012 vs. age 9 in 2011). This starting age is expected to continue trending downward, the research group said.

"The question becomes whether this mobile usage will continue to grow for 2 to 17 year olds, and if usage will become more prevalent than gaming on consoles and computers as time progresses," Callahan said. "More importantly, we need to understand how these forms of gaming provide different types of experiences for young gamers."

The Kids and Gaming 2013 study is based on the results of an online survey fielded from June 26-July 18 this year. It incorporates data from 3,842 children ages 2-17 who currently play games on any device.