Media playback is unsupported on your device Media caption Left behind child: 'When Mum and Dad come back to visit, I run to meet them... I run a very long way"

It has been an industrial revolution on steroids.

China has done in a few short decades what it took other countries the best part of a century to complete. And if the pace is extraordinary, then so too is the scale.

Britain had a population of around 10 million when its industrial revolution began - China's today, is more than a hundred times that size.

In the five years to 2013, China's construction industry poured as much cement and its banks lent as much money as the US did in the whole of the 20th Century.

So it should come as no surprise that the social dislocation accompanying this economic upheaval is of a degree that Charles Dickens couldn't have imagined in his wildest dreams.

And nothing highlights the human cost quite like the issue of China's left behind children.

One-fifth of all children in China

Tang Yuwen's story in the animation above is just one among many, many such stories.

His parents work in the textile mills in the city of Chengdu, dragged away from the village by the same forces that took their latter day British counterparts to Manchester a century ago.

The best current estimate suggests that more than 60 million children are growing up in the Chinese countryside while their parents live and work elsewhere, manning the assembly lines and operating the construction machinery at the heart of China's economic miracle.

That's one fifth of all the children in China and, in recent years, the country's state-run media appears to have been given license to discuss the tragic consequences.

In June 2015, four siblings - the youngest just five-years-old - whose parents had left home to work elsewhere killed themselves by consuming pesticide. The China Daily report makes clear it is not an isolated case.

'I miss them so much'

Tang Yuwen lives in the county of Sixian in Sichuan province with his grandmother, his younger brother and his two cousins.

During the week, they spend the time in a one-room apartment a short walk from school.

They're poor. They bathe in a metal tub placed on the floor in the centre of the room and they share a toilet with their neighbours.

All four boys are "left behind children" and over the decades, as millions of workers have streamed out of remote, rural Sichuan, theirs is a common experience.

In Sixian's primary school up to 80% of the pupils are live without their mums or dads.

Modern day China may have been built on the hard graft of its internal migrant labourers, but it has taken a heavy toll from their children too.

The bereavement is all too plain to hear in Tang Yuwen's interview.

"I know it is hard for mum and dad to earn money," he tells me, "but I miss them so much, it is very painful."

Read more on the transformation of China

In Guizhou province, not far from where the 2015 pesticide poisoning took place, we find 14-year-old Tao Lan, living with her 11-year-old brother, Tao Jinkun.

They are among perhaps China's most shocking child welfare statistic: more than two million left behind children are thought to be living alone, without the support of a close relative.

Media playback is unsupported on your device Media caption BBC's John Sudworth meets the Chinese children and parents living far apart

In a two-room home, with the wind blowing through the gaps in the wooden boards, Tao Lan helps her younger brother with his homework, she grows their own vegetables on a small patch outside and she cooks their meals.

The two take it in turns to wash the dishes.

Their parents live and work more than a thousand miles away, and come back just once a year.

"If you've had a bad day at school it must be very hard not to be able to talk to your mum and dad about it," I suggest to Tao Lan.

"I can't tell them," she replies, and then, wiping tears from her eyes: "Mum and Dad live a hard life, I don't want them to worry about me."

There is, of course, a now accepted view in the West that deprivation and childhood neglect can increase the likelihood of anti-social and criminal behaviour later in life.

Media playback is unsupported on your device Media caption Zhan Jiayue, 9, tells her story of life without her parents

But what strikes me when talking to the children we meet in Sichuan and Guizhou is not anger or resentment.

It is instead their readiness to accept with extraordinary maturity that their parents have had to make difficult choices out of economic necessity.

Even so they can't always hide the emotional cost, a tension most visible perhaps in our interview with nine-year-old Zhan Jiayue, a school-mate of Tang Yuwen's.

Spurred on no doubt by the mounting public concern, the government has decided that it needs to be seen to be acting.

It recently issued a new directive, reiterating existing laws against child abandonment and reminding local authorities of their duty to protect vulnerable children.

And now the authorities have announced that they will conduct a nationwide census, the first of its kind, in an attempt to gain a proper account of the number of left behind children.

But the truth is the efforts to enhance enforcement and to gather better data will not do much to address the root causes of the problem.

'I worry about his safety'

The textile factories in the city of Chengdu are just a few hours drive from Tang Yuwen's home village.

But the long hours and the need to save money mean his parents are able to travel home only two or three times a year at best. And yet the obvious solution, taking their children, with them is not an option.

Despite years on the production lines it is almost impossible for them to lose their official migrant status.

China's household registration system means that although they can work wherever they choose, they and their children can only exercise their welfare rights, including access to health care and education, in their home village.

It is a strict system that has allowed China to manage its population flows and, arguably, prevent a common scourge of other industrial revolutions elsewhere; slum developments as whole families flood into the cities in search of a better life.

In a restaurant close to their factories, we show Tang Yuwen's parents the interview we recorded with their son.

It feels an uncomfortable and somewhat cruel device, the kind beloved of TV news reporters in search of dramatic effect, but both parents are keen to see the video.

After all, they haven't seen Tang Yuwen for five months.

Tang Yujun laughs when he sees his 12-year-old boy dressed in formal attire, something I'd taken to be a small, personal flourish of eccentricity amid the drabness of village life. It turns out he's been rifling through Dad's wardrobe.

"That's my tie!" Mr Tang exclaims.

But again, the emotion is just below the surface and we soon glimpse the pain of the enforced separation, this time from the parents perspective, a pain multiplied tens of millions of times across this vast country.

"I'm so worried, because I'm not with him," his mother Liu Ting tells me through her tears. "I worry about his safety. If there were no legal barriers, we would bring him with us."

There is talk about reforming the household registration system, but it will be slow and selective and it is likely to keep the megacities of Beijing, Shanghai and even Chengdu where Tang Yuwen's parent work, out of the reach of many rural families.

The government admits the problem of left behind children is urgent. But for everyone who buys a made-in-China product, or who invests in this still-growing economy, there is a question worth asking.

If this super-sized industrial revolution had taken place within more democratic constraints, might the migrant workers at the centre of it all have been able to demand something fundamental, and so often taken for granted elsewhere?

And might they by now have won that right to a family life?