The problem is that covering miles and living off the land at the same time don’t mix very well. It sounds like those kids knew the jungle and knew what to eat. The jungle has a lot of food options if you know what’s safe and what’s not. And if they weren’t traveling far they could maximizes their search for calories while minimizing the burning of them.
In @Doug48 ’s scenario it would be hard to cover a lot of miles quickly while searching for food. If a person is in really good backpacking shape with their feet toughened up, not carrying too much weight and they have good footwear they could cover 20+ miles/day pretty easily walking trails or backroads. But that means hiking most of the day with little time for food gathering and avoiding threats. They will be burning at least 5000 to 6000 calories a day and drinking 2 or so gallons of water a day.
But most people (even the ones in very good shape) aren’t prepared for that kind of grind for more than a couple days in a row even if they can somehow miraculously find all that food and water without significant detours and pauses. Many hiking boots start breaking down before the 1000 mile mark leading to more foot issues.
The most calories I’ve been able to carry is about 25k. Which lasted me for 10 days and about 230 miles before I had to resupply in town eating all the food I could get my hands on before filling up my pack and starting on my next stretch. But I had the advantage of knowing where all the water sources were and where my next resupply would be and I didn’t have to avoid other desperate people.