It is not easy to shield the child but what we can and must always do is to equip the child to deal with them. From a very young age, through stories and rational explanation, children should be taught to discern between truth and its distortions, beautiful and refined vis a vis all that is crude and base, that which is really good and that which is harmful. He needs to be taught the importance of being truthful and the courage to say No to things that are harmful.
It is important to set for him an example since children tend to quickly imitate. It is no use asking the child to avoid negative things if in the house the elders speak lies, indulge in anger and quarrels and watch unhealthy programs or listen to all kinds of music that has no value except create excitement of the senses. A big source of negativity is the internet and we cannot expect them to be away from it if we are all the time on the phone.
What is most important is to be a living example of the qualities we want them to have and instead of teaching him how to avoid negative things, teach him how to be positive under every condition, situation and circumstances.
Affectionately,
Alok da.