This BBC radio programme may be of interest, but note that it will become unavailable in just a few days from the date of this post:
http://www.bbc.co.uk/programmes/b03m7mdc
It makes reference to the National Trust Natural Childhood report (http://www.bbc.co.uk/news/science-environment-17495032) and the Free Range Kids movement (http://www.freerangekids.com/).