This tool is - the dreaded TV.
Ok, I do limit the amount of TV watching that my children do. There are definate rules that they follow, and I do restrict the amount of watching. I also am very choosy about the shows that they watch.
That said, they do occasionally get to watch TV. I add just that little bit to the educational value of the TV by turning on the Closed Captioning. Almost all modern TV's, VCR's, DVD players, etc have a means to turn on the Closed Captioning - the words that appear on the bottom of the screen to tell deaf people what is being said. This makes the TV similar to listening to a book they are "reading" on a CD or MP3 player.
To increase the learning, once your children are starting to read a bit, let them watch a show with the volume off but the Closed Captioning turned on.
I had read a book that mentioned how almost all the children in one city in Europe were almost all fluent readers when they started school, because all their TV was in another language, with subtitles in their language. To watch TV, they either had to get very good at reading, or become very good at the other language.
I wouldn't say that this should ever be your only reading instruction - but that if your children are going to get to watch a TV show anyway, they may as well benefit that extra little bit.