Impact of TV on Kids

Caplan claims tv watching is large net positive because it reduces the cost of having kids and is essentially free. He argues the negative impact on say IQ is ultimately fairly minimal, based off evidence from twin studies.
http://www.med.umich.edu/yourchild/topics/tv presents some of the negative evidence for tv that's not controlled well for heredity. Claims typical 2-5 year olds watch about 4.5 hours of tv per day (and is 10 years dated, probably gone up due to tablets and phones).