The American Academy of Pediatrics recommends that children watch no TV up to the age of two. However, it is generally agreed that TV itself is not harmful to young children. Rather, it is bad for children to watch the wrong sort of content, or to watch a lot of TV.
The only TV young children should watch is high-quality educational TV, and they should only watch half an hour a day to one hour maximum. For babies, 10 to 15 minutes at a time is appropriate to begin with.
For more on this, read Television – Good or Bad on the BrillBaby site.