I totally agree with the fact that "kids are not allowed to use mobile phones until they turn 14". First of all, the thermal radiation of mobile phones that directly harm their eyes causes their eyesight to deteriorate. Second, it can distract students from learning, they spend time playing games, listening to music, etc...that forgetting about their tasks such as submitting assignments, doing the project. Furthermore, they have access to inappropriate information, and they might take pictures of others to share them on the web or use them to force people to do things for them. In conclusion, parents should let them use a mobile phone when they're over 14 so that they can be aware of their effective use.

(Hình như làm hơi quá thì phải :)), Good luck!