And that is to be an active parent and go camping, hunting, fishing with kids. Geocaching, bushwalking, kayaking, long distance bike rides etc.
These are some good starting lists: http://www.natureplaysa.org.au/resources/2/51-things-to-do-b... https://www.50things.org.uk/activity-list.aspx
When I was a kid, my over protective asian mother would let me out of the house when I got home from school, and I'd wander around the neighborhood with the neighborhood kids, and come back when it got dark.
My generation's (I'm 30) ideas of "proper parenting" are too god-damn time intensive. You should be doing stuff with your kids, sure, but beyond a pretty young age, it's their job to entertain themselves.
They go to playgrounds before and after school every day and play with other kids so it isn't like they don't get time to do their thing. My 4yo loves digging up the yard and build things in it which is great when I have a deadline. They have offcuts of wood and real hammers and nails at pre-school for my 4yo.
I really don't think my kids are wrapped in cotton wool. But there are boundaries. It is great for kids to have play areas where they can build stuff but kids also like to play sport, swim, learn music etc. I think sometimes ideas get romanticised and people lose perspective.
The operative part is that they're doing things not with you, learning to interact with each other and navigate challenges on their own terms, not their parents'. Outdoor activities are great, of course, but it is no better or worse than any other supervised activitiy.
A hundred years ago kids might go out with some other kids and learn some bushcraft or fishing or hunting. These days many of the other kids are housebound, often the ones I most wish my kids could be playing with.
I would rather my kids learn about the world constructively than play Lord of the Flies. They still play with other kids a lot and that is necessary, not sufficient. I would like my kids to get a balance of free unrestricted time and learning a bit of discipline and team work playing team sports and doing solo activities where they can learn some self-reliance. I think these articles romanticise one aspect of childhood to the exclusion of others.
I live in a small town and as soon as my kids can negotiate the roads safely they will have the run of it unrestricted but that doesn't mean that all they are going to do is hang out at a building site with old matresses and broken palletes. They will be riding to sports practice or the swimming pool, or skatepark or to go fishing.
Using the "gie a man a fish, teach a man to fish" idea, I'd say the gist of it is "Give a kid a fishing rod, and let's see what comes out of it".