TV ratings guru The Nielsen Company has turned its bean counters on to the tween mobile market in the US. Not surprisingly, use among the demo keeps growing and a full 35% of US tweens now own a mobile phone.

Neilsen’s upcoming report, Kids on the Go: Mobile Usage by U.S. Teens and Tweens, further estimates that 20% of tweens are sending text messages and 21% have used ring and answer tones over the past year.

Notably, the study found that only 5% of tweens access the internet via their phones each month, but those that do are more than willing to use their phones as a home-entertainment system. The majority (58%) of tweens who download or watch TV on their phone do so at home. And when it comes to downloading and playing music on their mobiles, 64% of tweens engaged in the activity also do it at home, while 56% of tweens who access the internet stick to their familial environs.

However, tweens still lag behind teens in cross-media use. Nielsen reports that tweens spend less time surfing the internet than their teen counterparts. The report states that 48% of US tweens said they spend less than one hour per day online, with 70% of tweens online using the internet for gaming. Comparatively, 81% of US teens say they spend one hour or more per day online, with email being the most pervasive online activity for this age group.