Fathers and mothers open the door of their children's room, and there they see them, late at night, alone, in front of a window of infinite possibilities. On the other side, a legion of software engineers and marketing experts work to keep them glued to the screen. The responsible use of the mobile seems like an unequal fight: willpower is not enough when we fight with algorithms and cutting-edge technology. Although the task is arduous, addressing a healthy coexistence with mobile technology is essential to achieve optimal emotional development in young people. This book tries to understand the concerns of children and adolescents, and provide possible answers to the dangers they may face. Sexting, grooming, cyberbullying, trolling, fraping… the list of threats is getting longer and longer. Before them, parents, often with a considerable digital divide, go with their tongues hanging out, trying to order all that reality that escapes them. On social networks, popularity is just a click away; Likes, smiles, hearts or comments are very tempting for many teenagers, which can distort their scale of values and foster a wrong perception of reality. The statistics are eloquent: children have mobile phones earlier and sooner and use them for many hours a day. However, there is no mathematical formula to ensure reasonable use of technologies. The culture of agreement, coordination between families and educational centers, the example of fathers and mothers, and legislation that knows how to adapt to the digital reality will be essential to face one of the most complex educational challenges of the 21st century.