A report in the Daily Mail shows how the roaming range of eight-year old children in one UK family narrowed over four generations, from 1919 to 2007. Great-grandfather Jack was allowed to walk six miles alone when he was eight, but eight-year-old Ed is only allowed to walk 300 yards to the end of his street by himself. 

It’s only one family, and I can’t find the report the story’s based on, but I accept the general idea that on average young children are much less independent now than their grandparents and great-grandparents were. They don’t walk or cycle by themselves nearly as often or as far.