A new survey has suggested that parents' fears over their children's safety is preventing those children from indulging in unsupervised play, and impacting on their opportunities to form bonds with friends. The survey is part of the Children's Society's Good Childhood Inquiry, and you can read a summary of the results online.
There has been so much research on various aspects of children's play that picking out just one or two suggestions for further reading is difficult. However, two recent documents which are worth a look are Neighbourhood Play and Community Action - which reports on a project to develop play opportunities in local neighbourhoods - and The Importance of Play in Promoting
Healthy Child Development and Maintaining Strong Parent-Child Bonds, a US report which approaches the topic from a pediatric's perspective. Further information on play in the UK can be obtained from the Children's Play Council.