The youngsters, aged 12 and 13, had spent six months creating the impressive structure between trees on land near Calverley Lane in Horsforth.
It had a watertight roof and terrace with a swing, laminate flooring and walls, and battery-operated lights, and contained a built-in table and a dartboard.
But when the boys arrived at the den to add the final touches by fitting a door and painting the walls, it had been incinerated and all their tools, including six hammers, a spade and brush and three saws, had been taken.
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One of the boys, Harry Bishop, 13, said: “We spent months building the den and we were really proud of it. We’d nearly finished it and we wanted to sleep in it when it was all done.
“I can’t believe someone burned it down - you could only see it if you went right into the woods. We worked so hard on it and now all our hard work has gone up in flames.”
Another of the young builders, Cristian Walker, 13, said: “There was no sign saying it was on private land - we don’t know if it was or not - and if someone wanted us to take it down, why didn’t they just say? We would have taken it down and used the materials to build the den somewhere else.
“We’re all so upset about it. We really enjoyed building it – it was very strong and we did it all by ourselves. None of us understand why someone would destroy it like this.”
Lisa Walker, Cristian’s mum, said: “I feel so sorry for the boys - they were really proud of their den, and all of us parents loved it because instead of staring at screens all the time the kids were out building a den in the woods - it was good old-fashioned fun, and they weren’t harming anyone. Youngsters today are constantly criticised for just staring at screens and not playing outdoors, yet when they use their initiative and create a great little den in the woods, this is the way they’re repaid.”
The boys now want to build another den, and are looking for suitable local land for their ‘phoenix’ construction, plus any donations of scrap wood, nails and tools.
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