Child’s play: “An easy task,” sniff the dictionaries. “Something that is insignificant.” Such definitions are not only wrong – they are a danger. However messy and mucky and mysterious to the hovering adult, play is vital to the child. Yet most of the UK gives it no priority: councils shut hundreds of playgrounds, year after year; property developers throw up expensive boxes with as little green space as they can possibly get away with; and schools squeeze playtime to cram in more lessons. Who cares? It’s only child’s play! Under such a regime, play is treated as a luxury good, and we know what happens to luxuries: they become unaffordable to those without money.

But there is one giant exception. I came to Flintshire, in north Wales, to research a piece on food poverty. While delivering hot lunches to local playgroups, we pulled up at Quayplay, in Connah’s Quay, and walked straight into the organised pandemonium of 140 children at play. Over the slope were strewn bits of cardboard that had been ripped up and turned into sleds. Right up ahead was a yard full of children wielding saws and hammers and knocking together bits of wood. Plenty of adults could be seen over the site, but they gave the children all the space they needed. What were they making? A set for a horror game, explained one boy, kindly enough but with an air of abstraction. He had better things to do than humour visiting reporters.

Welsh law puts every blueprint for a new housing estate or bypass under scrutiny for how it will affect children’s play

In one hall, a big circle was playing wink murder, while off to the side was the “sensory room”, for those with learning difficulties: soft music played, and a boy of about nine kept getting up and walking over to a support worker for a cuddle. Outside, another worker painted vampire faces, a tent was devoted to handicrafts, and 22 boys and girls chased a football. Every bit of this was free. “The day I charge parents for their kids to play, I’ll give it up,” said the senior coach, Steve Taylor.

The wood came from a local sawmill, the cardboard boxes from the local Morrisons. In similar fashion, the money to run the entire play-centre had been found out of grants and loose change from other budgets. Taylor remarked: “If it wasn’t for Janet, nothing would happen.”

The county council’s Janet Roberts stood at the top of the hill, beaming. “We’re creating memories here!” In an area where one in three households live below the breadline, “Some of these kids aren’t going on holiday. This is it. This is summer. So we’re going to make it as amazing as possible.”

Flintshire isn’t rolling in money, so how has Roberts managed to put on 70 playgroups on each day of the holidays? Simple. The play development officer and her colleagues on the council lean on the law. The UN gave every child the right to play, but the first country in the world to turn that into law was Wales.

Every Welsh local authority “must secure sufficient play opportunities in its area for children”, according to the measure passed by Cardiff’s parliamentarians in 2010. It is, says Mike Barclay, who used to do Roberts’s job in neighbouring Wrexham, “a beautiful piece of legislation”. It encourages councils to ask children what events and activities they want, and to reflect their desires in annual play action plans. It puts every blueprint for a new housing estate or plan for a bypass under scrutiny for how it will affect children’s play. And it gives play officers like Roberts extra ammo when they need cash to organise aquaslides. It makes Wales the first country in the world to take play seriously.

The law does have some artful vagueness, the odd “sufficient” and “so far as reasonably practicable”. Nor has it protected play-centres from the spending cuts that have scarred the past decade. But contrast the Welsh government’s commitment with Westminster’s casual neglect of children – when David Cameron took office in 2010, he ripped up Labour’s play strategy, then slashed the budgets for Sure Starts, for benefits for working parents, for local councils. The result has been devastating.

More than 4 million children live in poverty today – more than one in four of all under-18s – up from 1.6 million at the start of the coalition. Through freedom of information requests, we know that councils in England closed 214 playgrounds in just two financial years in the middle of this decade, and there are plans to close a further 234. Up and down the country, local youth services have been cut to ribbons. Children can still use play spaces – but increasingly their parents will have to pay. The emblematic example is the adventure playground in Battersea, south London. Until very recently, Britain was a world leader in adventure playgrounds and the one in Battersea was excellent. Free to all, it was shut by Tory-run Wandsworth council in 2012. Its major replacement is a Go Ape centre, where a “Tree Top Adventure” lasting two to three hours will cost an adult and two 16-year-olds £108.

Britain’s politicians are ignoring child poverty. The result: it’s soaring | Dan Corry Read more

And while the grownups were doing all this, they also turned children into walking problems. In London, kids are painted either as members of violent gangs or as targets of them. At the same time, more than 81 youth centres and projects have disappeared since the riots of 2011. Across the country, they are supposedly morbidly obese, or in a sexting frenzy, or massacring each other in computer games, when what they should really be doing is preparing for their never-ending exams.

Yet play teaches children to resolve differences. A child who has problems in the classroom can turn into an exemplar in the playground. Most of all, it gives children space to be themselves among their peers without being pulled and prodded and measured by adults. The rest of the UK should follow Wales’s example, by making play a legally protected right for children and backing that commitment with the relatively small amount of cash needed to run decent play services.

At Quayplay, Steve Taylor blew the whistle on another epic game of football. “These kids are our future,” he said. “Here they learn respect. How to handle great highs and big lows: they learn all that here. And when they go home they’re not playing on a tablet – they’re too tired. They sleep soundly.”

• Aditya Chakrabortty is a Guardian columnist and senior economics commentator