That's not causation, though. Parents who let their kids watch a lot of TV may also be less likely to act against bad behavior (by disciplining them, providing better models for behavior, and so forth). A large amount of TV-watching time could simply be an indicator of poor parenting, rather than the actual cause of bad behavior. I don't know whether or not this is the case, but I'm wary of studies that only look at surface-level correlations.

Edit: However, after a bit of searching I found this page which summarizes several results that go beyond basic correlation.