I wonder what specifically has changed in the last 30+ years though? Is it technology keeping kids in because it is more attractive than climbing a tree? Or changing attitudes to risk communicated through the news, schools or parents themselves?
I spent my formative years walking, cycling and exploring but, I think, I had the advantage over a lot of people in living on the outskirts of a town with friends that lived on farms. It was a lot easier for me to jump on a bike and head out than it was for a lot of my friends in town. Come to think of it, I didn’t get a computer until after I had left home. When I did get one I stayed in a lot more. That could have played a huge part.