I agree with Joan. Each parent must come to their own conclusion/what they're comfortable with, but I know there are studies that show that children under 3 who watch tv tend to have a harder time concentrating later in life, amongst other things. It also is better for their eyesight development to stay away from the tv until older. I think one or two hours a week probably wouldn't hurt, but I personally wouldn't do more than that. (If I ever have kids they'll watch dvds of Sesame Street and Mr Rogers or Bill Nye, etc.
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