IELTS Essay: Television and Children

'It is no secret to say...' sounds better I think. Although what you have written is not wrong. 

The influence of television on children has always been a matter of controversy. Some people say that what they watch on TV influences their behavior while others say the amount of time spent watching TV influences their behavior.

Both points of view are equally valid in a certain context

Both 'viewpoints' sounds a bit better.

Some analysts and social psychologists have conducted studies about the influence of television on the behavior of children. Many experts argue that children tend to repeat what they watch on the screen and that they are always looking for role models. That is why television content can sometimes be counterproductive.

'Counterproductive' isn't a great word choice here. Maybe: television content can sometimes have a detrimental effect on our children's psyche.

For example, if a child constantly watches programs with violent content, they will probably develop aggressive behavior.

On the other hand, the amount of time watching television is an important variable to consider. Research indicates that children who spend a lot of time watching television can present social problems since they prefer to see cartoons to play or spend time with their friends. Also, these children may have low grades.

This is a bit unclear. Do you mean that lots of time watching TV causes social problems since they prefer to watch cartoons rather than play with their friends?

In short, everything in excess is bad. Parents and teachers must be key players in the development of a child

'parents and teachers ought to act as role models for our children's development' sounds better

and therefore they should care about them and not be negligent. I think that parents should maintain control over television content, today there are many ways to censor inappropriate content on a television. There are Parents Guides as well. On the other hand, parents and teachers must promote other types of activities for children that contribute to their education and development.