There have been a lot of discussions about whether television has positive or negative effects on children. Unfortunately, there is no good case that can give us a powerful argument. I believe it can be positive if parents can see it as a tool and use it well.
Let children watch natural programs such as documentaries can encourage children to see the wide world around them. This can build their curiosity, which adults will find very important when they grow up. It is alright even if children can't understand what these programmes mean, because we can't expect them to learn everything before they go to school.
Furthermore, one of the most crucial things a young child should learn is language, especially their mother tongue. This responsibility is mostly taken by the parents of the children. But television programs also build up our talking ability, such as cartoons.
One the other hand, many television programs bring no help to children, cartoons give nothing useful to children except the language that I have mentioned above. Soap operas can sometimes be so complex that they cannot understand. The scariest part of this is that children with real curiosity usually find what the words those adults say actually mean. This may cause them to grow up much faster, which is the result any parents don't want to see. Action movies always make a reason violent, that may be a bad habit that lasts for years.
In conclusion, when television is a tool, it is usually good if parents can use it for their education.