What hiking trail allows this? Going off-trail, digging, climbing, and building will all get you booted. These are natural environments where the trail is already a significant compromise to justify the preservation.
There is a park in my neighborhood, half of which is designated as a nature play space. Where all those things are allowed, lots of forts. It appears it was associated with the national wildlife federation natural learning initiative.
https://www.nwf.org/Kids-and-Family/Connecting-Kids-and-Natu...
Nature play spaces are common in Australian schools now. Logs, rocks, dirt. Kids make forts and grind up rocks and so on. 40 years ago at the same school, we had old car tyres to roll around.
But I think there must be a misunderstanding, as it would be unusual for a place near suburbia to be a national park or similar area with restrictions like this.
There's nothing there I can see in the NT park rules that precludes digging or building a fort.
Around the world some place back onto national parks, other places have large areas of undeveloped land that aren't national parks (cattle stations, community land, etc).
The video I linked is representative of the kind of ocean land I grew up on and still live near part time - it's a good place to raise children, plenty to do.
I had some experiences like this thanks to boy scouts, but it was on private land owned by another family for timber, or at a summer camp hardly an everyday thing though. Depending on what you're doing/season/location national forests allow gathering wood and stuff for building fires.
