Human development is not only affected by our biological feature inherited from our parents but also environment around us. The environment elements include both social environment and family environment. Environment effect on human is more reflected on behaviors, however, how much does it involved are still under research without a solid conclusion. Most of the time, researchers use twin studies to compare how different environment affect one's behavior and personality.
According to Piaget, we won't achieve our most abstract levels of reasoning ability until our adolescence and our frontal lobe which in charge of our planning, decision making and impulse control is still in maturing process and that's is why teenage kids are easier to be influenced. Both social environment and family environment could affect our cognitive development during this time and that is the reason why the society will put that much efforts in publicize protecting adolescence from improperly internet content and home violence.
Along with the development of the entertainment industry, child and adolescences are exposure to media much more than last generation was. How TV program and computer games affect their behavior becomes more and more complicated because more factors needed to be considered to have valid result. As far as I concern, ways of how does violence and sexual content exposure to child needs to be separately examed. Also, for different age level, children are affected differently. What's more, for oriental and western culture based education, child may reflects differently to same content.
Here is some links related to study on this area.