Dont forget tree houses- we had a mutant maple tree that had 4 trunks. My dad got into the middle of those and reaching as far as he could nailed two 2x6 boards across each pair. When done he hands me the hammer and says something like 'now it's your turn, what can you do'?
I was about 10....
Boy he regretted that- we raided his garage, the neighbors trash piles, house construction sites and everything else and built that thing up to 3 stories, I'm afraid of heights, my little brother isn't- Kevin climbed as high as he could in the tree and nailed a couple of short boards way past the point where the tree would support my weight.
from there we would punish the neighborhood with crabapple loaded sling shots and grenades from magnolia cones! We made spears out of the center sprout of those big sticker plants whose name I can't remember. And none of us died or was seriously hurt!
And all this ^^^ took place over our sand box- Dad had gone out and bought a truck load of cross ties and sectioned off parts of the yard with them. he boxed in the area under the maples and filled it with sand and we in return filled it with metal Tonka trucks and pieces of dead Gi Joes who didn't survive whatever war they were fighting.
meanwhile the cats in the neighborhood filled it with their nutty buddies- lol- they were there constantly, much to the delight of my Shepard and later my Weimeraner.
And we didn't get sick either.
Kids today just don't get it.