New research indicates that on average, children in the U.S. are exposed to nearly four hours of background TV a day. Previous studies suggest television exposure has been linked to children being less likely to pay attention during playtime, reduced cognitive abilities, and lower-quality interactions between parents and their children:
http://www.huffingtonpost.com/2012/10/01/children-tv-exposure-study_n_1923719.html
http://www.cnn.com/2012/10/01/health/kids-background-tv/index.html