Such is the upside-down, topsy-turvy state of our world, that the children are now the adults and the adults are the children. In Westminster, our supposed leaders – men and women of mature vintage – keep stamping their feet and demanding what no one can give them.

They insist they should be allowed to gobble up all the birthday cake and still have cake left to eat, threatening to storm out of the European Union and slam the door behind them. As Dominic Grieve, the former attorney general, rightly puts it: “Threatening to leave is the behaviour of a three-year-old who says that they are going to hold their breath if they do not get the toy that they want.”

In Washington, meanwhile, Donald Trump, aged 72 and three-quarters, has screamed and screamed and screamed until he is sick, pounding his little fist on the table as he demands money for the big wall of bricks he wants to build, and today declaring a national emergency to get his way. The House speaker, Democrat Nancy Pelosi, assessed the situation accurately last month, when Trump was shutting down the government: “It’s a temper tantrum by the president. I’m the mother of five, grandmother of nine. I know a temper tantrum when I see one.”

But perhaps these comparisons are unfair – not to Trump or the Brexiters, but to children. Because while Trump has invented a wholly fake emergency – there is no threat of imminent invasion by migrants on the US’s southern border – and while the threat of a no-deal crashout from the EU is, if all too real, entirely avoidable via a simple vote of the House of Commons, it has fallen to children to point to the emergency that is neither fake nor easily averted. It has fallen to those so young they are not trusted to decide what they can eat or when they can go to bed to sound the alarm about the crisis that matters most: the crisis of the climate.

'The beginning of great change': Greta Thunberg hails school climate strikes Read more

What are we to make of today’s strike by schoolchildren, in Britain and across the world, part of a rapidly growing movement aiming for a global walkout of kids on 15 March? How should we react to a phenomenon that began with a single child, a Stockholm teenager by the name of Greta Thunberg, who skipped class one Friday last August to sit in protest on the steps of the Swedish parliament, and which today saw primary-aged children, as well as teenagers, following her lead, wielding placards as they marched in Parliament Square and the streets of dozens of British towns and cities?

At first sight the reaction surely has to be one of unfettered joy. Many will share the enthusiasm of those veteran environmentalists hailing this as the most exciting, most hopeful development they have witnessed in decades of campaigning. A young generation so easily caricatured as disconnected and self-absorbed, heads tilted permanently downward towards their phones, Instagramming pictures of themselves, are instead taking a moral lead.

Liberal parents have been beside themselves with pride, bundling up their little ones in scarves and gloves as they watch them bunk off school to save the planet. I suspect there will be many Guardian readers who shared the dilemma I myself faced this week. Not whether to allow their kids to miss lessons in an exam year for the higher cause of tackling climate change: that one was a no-brainer. No, the dilemma I have in mind is rather more finely balanced. Should the conscientious liberal parent reveal their excitement about seeing their son or daughter take a stand, or should they pretend to disapprove, thereby supplying their young with the thrill of principled rebellion?

Teachers have grappled with the tension between the law, which says that children must be in school, and the obvious truth that this is a “teachable moment”, a learning experience. In fact, the law says children must be in school unless there are “exceptional circumstances”. As the country’s sole Green MP, Caroline Lucas, told me while marvelling at child protesters on the streets in her Brighton constituency: “When David Attenborough is warning that the future of civilisation is at risk, that counts as ‘exceptional circumstances’.”

Play Video 1:20 Thousands of UK students strike over climate change – video

It’s not just the case against carbon emissions that this moment can teach. Thunberg is also demonstrating the power of the individual act. It’s so easy to feel impotent given the sheer scale of the climate crisis. But Thunberg, whose Twitter bio describes her as a “16-year-old climate activist with Asperger”, is the living embodiment of the case against defeatism. Rabbi Jonathan Wittenberg, an early and tireless environmental advocate, is right to say that the #FridaysForFuture movement is “not the first great change to begin with the action of just one person”: from Abraham onwards, our history and tradition is full of people who, alone at first, changed the world.

All of these are reasons to be heartened. And yet, there is a harsher truth to face. These demonstrations by the young are a terrible indictment of the rest of us. They are a mark of our failure. Their action is only necessary because we have failed to act. As one placard at the Belgian protests told politicians: “I’ll do my homework when you do yours.”

This week marked the first anniversary of the Parkland school shooting in Florida, a massacre of 17 that led to a mass movement of young Americans demanding gun control. That effort too is a product of failure, children having to act because adults have failed in their basic duty: to protect the young. There was great poignancy in Thunberg’s words to the UN climate change conference in Poland in December: “You are not mature enough to tell it like it is – even that burden you leave to us children.” Any delight, pride or joy we feel in these protests has to be tempered by the realisation of the adult world’s failure.

My generation trashed the planet. So I salute the children striking back | George Monbiot Read more

There’s a last question, one that feels unfair given the idealism written on the faces of these children. Will this effort work? The sceptic will say not, speculating that the attention of the young is a fickle thing, that this will be – as parents have told their kids through the ages – just a phase. They might also add that the powerful are very skilled at co-opting, and thereby often neutralising, the young: witness Thunberg’s recent invitation to Davos.

What’s more, polling suggests there’s not much in the way of heightened environmental consciousness among the young. According to Ipsos Mori, only 12% of 18- to 24-year-olds named the environment or pollution as an important, or the most important, issue facing the country – no higher or lower than the overall average. Ipsos Mori’s Ben Page reckons that until kids are blocking the roads in most towns, this latest effort “won’t cut through”.

I’m more hopeful than that. There are signs that the climate crisis is finally getting the attention it deserves. Watch would-be Democratic challengers to Trump in 2020 fall over themselves to embrace the “green New Deal”, a vision of transforming the economy to save the planet with appeal beyond those who have previously tended to prioritise the environment. Watch too the way the Extinction Rebellion has captured the imagination; or the reaction to news that the world’s insect population is plummeting, a destruction that threatens the collapse of nature itself.

Page warns that humans are exceptionally bad at spotting slow, long-term dangers: “We’re wired for sabre-toothed tigers,” he says. We can find it hard to envisage the future. The only way we can visualise it, perhaps, is through our children. When they tell us we are burning their future, as they are now, we have to overcome our shame at having failed them – and listen.

• Jonathan Freedland is a Guardian columnist