Edit: I apologize for the rudeness of my comment. However, it is my understanding that the evidence available today points to things like TV being damaging to the development of the very young (1-3 years old)
When it comes to television, studies have shown some negative correlation. But they disappear when you adjust for socioeconomic status and parental education: http://www.cnn.com/2009/HEALTH/03/03/babies.watch.TV.
What the data really indicates is that poor people and single parents let their kids watch more TV, and since IQ is highly heritable, TV watching ends up being linked to lower cognitive performance. But it doesn't seem to be a causal relationship, or at least the data doesn't clearly support that conclusion.
Obviously its important to engage with kids, and parking them in front of an iPad could get in the way of that. But at the end of the day, there are no prizes for making parenting harder than it already is.
There's not much science. That science is poorly reported by mass media. It's misunderstood by many readers. And most people have fierce cognitive biases anyway.
Basically, "talk to your children. watching tv stops you talking to your children". I guess that's reasonable, except you can't talk constantly at children. Not everything is a learning opportunity. The parents and the children need some down time. The science doesn't say anything about exhausted stressed parents deprived of human contact and the impact that has on children, or the possible benefits of TV to that parent.