In 1975, Roger Hart conducted a study on where children felt safe to play. He focused on 86 children between the ages of three to twelve in a small town in Vermont. Hart would follow the kids throughout the day, documenting everywhere the children went by themselves. He then took that information and made physical maps that measured the distance each child was allowed to go by themselves and what the average was for every age group.

Hart discovered that these kids had remarkable freedom. Even four- or five-year-olds, traveled unsupervised throughout their neighborhoods, and by the time they were 10, most of the kids had the run of the entire town. And the kids' parents weren't worried either.

Then several years ago (about 2014), he went back to the same town to document the children of the children that he had originally tracked in the '70s, and when he asked the new generation of kids to show him where they played alone, what he found floored him. Hart said, "They just didn't have very far to take me, just walking around their property." In other words, the huge circle of freedom on the maps had grown tiny.

Hart added, "There is no free range outdoors. Even when the kids are older, parents now say, 'I need to know where you are at all times.'" But what's odd about all of this, is that the town is not more dangerous than it was before. There's literally no more crime today than there was 40 years ago.

So why has the invisible leash between parent and child tightened so much? Hart says it was absolutely clear from his interviews. The reason was fear. Here's the conclusion to his new study: fear of the world outside our door narrows the circle of our lives.