What should we teach our kids?

When you have kids, there is just so much in your mind. Everyday they learn, as if their brain cells are craving for more knowledge. I am starting to teaching my boy the meaning of "NO" but I am not sure if I should be disciplining him if he doesn't listen. He is just 17 months old. And when should we start shielding our kids from the negative things ... like TV commercials, candies, Internet and etc)? I am telling you my boy already loves the internet, especially those children games sites. There is a parenting debate forum going on about this topic if you are interested to find out more. All I can say, it is not easy to be a parent.