The child's freedom of movement--what are the consequences of its loss?

Provocative British transportation thinker Mayer Hillman gave a presentation entitled "The Impact Of Transport Policy On Children's Development":

Some years ago, the government transport minister at the time referred to the extent of car ownership as a barometer of freedom. What does that barometer show for children? Over the last 30 years at least, owing to a concern for their safety, this has been steadily diminished by parental restrictions imposed on their being out and about on their own. More and more of them are escorted on their leisure and school journeys - and up to an ever-later age in their childhood. This may well be having a detrimental effect on their social and emotional development as well as, more obviously, on their physical development. It is as if a malign dictator intent on harming society by picking on its most vulnerable and important members was achieving his ends by promoting activities which make the environment unsafe for children to be out on their own; encouraging parents and their children not only to be aware of the dangers but to make them feel that they are more at risk than they are in practice; and depriving them of opportunities for improving their health and acquiring these coping skills.