The Research Centers have loads on this, yet, the articles and information included here offer some nuances and perspectives not readily included elsewhere.

Three New York Times Articles: 
If Your Kids Are Awake, They’re Probably Online
An Ugly Toll of Technology: Impatience and Forgetfulness
A boot camp cure for web obsession

Huffington Post Article
What Do I Do About Screen Time?

 

 

 

Orion Magazine article entitled:
Why Children Shouldn’t Have the World at Their Fingertips

   

Kids exposed to 4 hours of background media a day

Not directly being attended to, but exposed -- within eye/ear shot. 
Consumption Digital DivideChildren from lower economic levels watch more, waste more time, perhaps due to parental availability or monitoring.