I think children should not watch a lot of TV.
Though TV in moderation can be a good educator as there are a lot of good educational programs which help children to learn the alphabet, numbers, about wildlife, time spending in front of TV should be supervised and limited depending on the age of child.
To begin with, unlimited time spending on watching TV has negative influence on children health: less physical outdoor activities, sore eyes. A lot of children also fall into a bad habit of eating while watching television.
Secondly, watching TV is a passive learning: a mind is not challenged, no creativity or using imagination. A child simply receives the proceeded information.
Thirdly, nowadays TV is full of violence. A child can’t see the difference between reality and fantasy and he is more likely to imitate what he sees. It also can cause confusion for a child in difference between what is right and what is wrong. “A bad guy” is a hero who often doesn’t take any responsibility and not always punished for his actions.
Also, spending a lot of time in front of TV doesn’t help children to develop or improve their communication skills. They less interact with friends, family. It also “steals” time from developing hobbies, improving reading skills,
Watching too much TV can lead to loss of ability to concentrate. Children get bored by real life where they need to apply efforts to concentrate on what they see and hear, think and analyze the received information. So, they prefer to watch TV because they can make a pause, rewind or skip the episodes they find boring.
For mentioned above reasons, I think it is important to monitor how much time a child spends in front of TV and be aware of what programs their children watch.