Well there are bad and good things that television effects children.....
the bad ones are that, if they watch near the television and without proper light, they're eyesight will get bad, they might pick out bad attitudes an bad languages in the shows and might act the same actions their favorite character acts in the shows. The good ones are that they learn things from watching TV shows, like friendship is important, looks aren't everything, some TV shows could help them build their self-esteem, it could build their hopes and faiths. For example, the show Naruto from Cartoon Network, even though there's a lot of fighting and blood, it still have the right lessons through every episodes.....to never give up, to never lose hope, to never let anyone bring you down. Through every episodes of any kind of TV shows, there's a lesson that children need to learn. Well, that's actually all i can tell ya, i hope i helped you....;)
There are some great kid's programs on TV and also Learning channels for children. Put a lock on the TV so your children can only get these certain channels. Most of the channels on TV are crime, blood, guts, gore and more gore, so it's best to supervise what your children see.
It's also important that your children only get 1 - 2 hours a day of TV and it's healthier for them to be inter acting with their peers and getting out in the fresh air as well as having quality time with family (doing things together.)