In China, 190 children are snatched every day - more than twice the number taken in England and Wales in a year. The Chinese government does not acknowledge the extent of the problem, or the cause. The Single Child Policy has made it essential to have a son, leading to the abortion of more than 40 million girls and setting the price on a boy's head at more than six months' wages. By Clare Dwyer Hogg

The events of this summer mean that every one of us will have considered, for a moment at least, the horror of having a child snatched. The emotions parents must endure aren't hard to imagine: the creeping numbness of realisation; the shock turning to panic as the minutes tick by; the helpless reliance on the goodwill of others, particularly the police. In Europe, the cases of child kidnapping are sporadic. In China, however, they are increasingly common. Around 190 children are snatched every day - stolen from their beds and the streets. This is more than double the average number of abductions recorded in England and Wales over a whole year. If 190 people were dying every day from the same illness, you'd call it an epidemic. And that's exactly what it is, except nobody really wants to talk about it. Especially the Chinese government.

The government doesn't want to talk about it because it's a short step from fully acknowledging the kidnappings to having to address why they're happening. Which means entering dangerous territory - a root cause of such large numbers of children being snatched is the fact that having a son in China is a necessity. He carries the family name, he is the child who will provide for his parents as they age. A daughter will leave the family to marry into another name, passively obliterating her own family line and leaving her relatives without the assurance of help in old age. The One Child Policy - which Save The Children calls a 'mass, live experiment in family life which is unique in the history of the world' - has resulted in prohibitive family-planning laws in China: prospective parents must have a birth permit before conceiving, and while rural families are allowed a second child if their first is a girl, urban families must pay a fine for flouting the one-child rule. And if you haven't had an abortion to get rid of your female child (although it is now illegal, around 40m girls have been selectively aborted since the One Child Policy was instituted in 1979), how can you be sure to get a son? Sometimes the only choice seems to be to buy a stolen child, gender already determined.

'I did think about suicide,' says Li, a woman in her early twenties. 'I missed my child so much.' It has been a year and a half since her little boy, Chen Jie, was taken. He was five years old, playing at his grandmother's vegetable stall in Sichuan, when Zhang, a trusted neighbour, passed by. Offering to bring Chen Jie back to his mother - and persuading the reluctant boy with the promise of sweets - Zhang left, taking the child with him. This was the last time Chen Jie was seen by his family. Later, when parents and grandmother realised that neither had the little boy, they ran to Zhang's door, desperately hoping he was there. Calmly, Zhang claimed that after giving him money for sweets, he'd left Chen Jie at the apartment block. Their suspicion of his involvement in their son's disappearance could not be translated into evidence - even though when the grandmother confronted him later, she said he yelled, 'I sold the kid, OK?' After police questioning, however, Zhang was free to go about his normal business, unlike the Chens.

'Sometimes I don't want to carry on my life,' Li continues. She has come close to killing herself many times, she says, but is always stopped by the thought of how disappointed her family would be. Culturally, the responsibility for the family weighs heavily: Li and her husband, Lung, already feel they have let their parents down by depriving them of the grandson who would carry on the family name. Once, Li admits, she was ready to jump from the top of a public washroom, but the owner of the building dragged her home. 'She tried to prevent me from thinking that way,' Li says. 'She knew a story in which a mother who lost her child killed herself by jumping off a building. After her death, the father sold the house and lost contact with everyone. Never came back. Later, their friend found the child and brought him home, but the whole family was gone.' Li has thought about this tragic twist many times. 'If you die, and your child comes back one day, he loses his mother forever.'

Li and Lung Chen are determined to do anything to get their son back, but their options are severely limited. The media is too close to the government to be used as a tool, and even joining a parents' support group must be done in secret. They saved up 600RMB - that's £40 - to put Chen Jie's picture on a poker set that features missing children on every card; in their desperation they're gambling on gamblers. Putting up 'missing' posters of Chen Jie, his eyes staring out brightly even from a photocopy, was risky because it's forbidden (the authorities aren't keen to have the reminder of missing children on show), but they did it. Hiring a private detective cost money, but they did that, because the detective has a reputation for successful rescue missions. Speaking to Westerners about their plight was downright dangerous, but they've done that, too.

The production team behind the Emmy Award-winning documentary The Dying Rooms, which in 1995 uncovered the neglect of abandoned children in Chinese state-run orphanages, went back to China this year. The idea behind the first documentary was that China's One Child Policy, the population stabiliser, had led to the abandonment of girls - this, and their subsequent abuse in some cases, was recorded as tragic confirmation. More than 10 years later, the team - this time headed by debut director Jezza Neumann - went back to investigate another consequence of the One Child Policy: the tens of thousands of Chinese children being trafficked every year.

Needless to say, if you're making a documentary about child abduction, looking for the abductors, the need for undercover filming is paramount. Sim cards were changed after every call; the production team met to discuss plans in locations that had plenty of exits; they all arrived and left from different directions. The Chinese word for Westerner is gwailo, a once derogatory term, which can be translated as 'ghost man': Neumann says his mission was to take this phrase literally. It's hard to render yourself unnoticeable as a Westerner with a camera in China, but he and his team tried to move through the country like ghosts, as unseen as the people they were searching for. The Chinese authorities, loath to let such stories out, are also extremely vigilant, and getting people to talk about their experiences of having a child stolen is virtually impossible. The air hangs thick with the threat of official reprisals and punishment. One potential interviewee whose son was stolen was visited by the secret police the day after a researcher had been to ask him questions. He backed out, too scared to commit to camera what he felt, too frightened to enlist the help of outsiders in such a close-knit community, where anything unusual gets back to officials - apart from, it would seem, the identity of child kidnappers.

The Chens knew the danger, too, but, thirsty for help, they agreed. It's not that the Chinese government doesn't report on child trafficking: there is coverage of rescue successes, or assurances that the government is doing all it can to combat the criminals. The stories are often, however, conspicuously free from statistics or analysis. Save the Children reports that last year Chinese officials from the Ministry of Public Security put overall trafficking figures (for women and children) at 2,500. This is much lower than NGOs estimate, but it's all about semantics, of course. International law - the UN's Palermo Protocol of 2000 - defines trafficking not only by the use of force or manipulation, but also as 'the abuse of power or of a position of vulnerability'. A child is any person under the age of 18. The Chinese government is currently drafting a National Plan of Action against Trafficking but, as it stands, the Chinese definition is much narrower. Article 240 of the Criminal Law of the People's Republic of China makes illegal the abduction of women and children (men are overlooked) for the purpose of selling. There is no clause for abduction without being sold - if you are taken away to be a slave or a sex worker, that doesn't count. And currently, if you are abducted at 14 in China, you are an adult, and not part of the statistics.

Chen Jie is very much part of the statistics - one stolen child in the mass of 70,000 snatched every year. His little life had already been fraught with difficulty. He was born a year after the Chens started seeing each other: the One Child Policy stipulates that children cannot be born without a birth permit, and you cannot have a birth permit if you don't have a marriage certificate. So Li had him in secret, giving birth in her mother's pigsty. Li and Lung hid their little boy for a year until they came to a decision that without a birth permit, without an official existence, Chen Jie's life would be nothing. They confessed to the authorities, and were ordered to pay a fine of 8,000 RMB (£520). They only finished paying that debt last year. Now, the strain of being left without the son for whom they struggled is palpable. 'It has been very difficult,' Li says, via a translator, speaking on a crackling line from their tiny apartment in the migrant workers' ghetto. 'We quarrel from time to time, but every time we think of our child, we remember we share the same goal. I already feel responsible and guilty. We don't want Chen Jie to come back to a broken family.'

The strength to stay together - like the rejection of suicide - is fuelled by the need to believe that they are maintaining a home for their missing boy, having in readiness a place for him to return to, and parents who are loving and at peace. This hope, no matter how tenuous, is some sort of light for the way ahead, even if at times it seems only to emphasise the darkening shadows all around. Depression floors them, guilt for letting their families down punctures their faith, and time has not been a healer. The detective, while active, is not getting any leads. They are - as the Chinese phrase goes - 'looking for a needle in an ocean'.

Part of the Chens' problem, and the problem for many parents like them, is that they are up against a highly organised criminal network which supplies a seemingly never-ending demand. Add to the mix that the moral code is skewed when it comes to 'adopting' (buying) children. If you were caught buying a child in the UK, you would be charged with child trafficking. Yet in China - as incongruous as it may seem - while it is illegal to abandon, steal or sell a child, it is not necessarily illegal to buy one. CCTV, a government-sponsored news outlet, recently reported that: 'Under the current law for families that adopt trafficked children, if they have not abused the children, and have not obstructed the rescue operations, the law enforcement can choose not to press charges, not to pursue further. Many parents of missing children find that unacceptable.' Parents of stolen children are immediately on the back foot; the law is essentially non-punitive, so child traffickers can justify their actions - they are simply supplying a demand that is not, in itself, a crime. Except, of course, it is. People buying a child have no guarantee that the child was willingly given up by his parents. And when the motivator for providing that child is money, reassurances mean nothing. A boy can fetch around 10,000 RMB (£650) which is a lot of money for one 'job', when you consider that a skilled production worker in China earns £1,200 a year.

One trafficker explains how he and his cohorts would identify the suitability of a child through the vulnerability of his mother. They would watch, wait, take a note of her routines, and bide their time for that moment when she would leave her son unattended. One such prize, he says, happened when the child was in bed, and the mother nipped out, unaware of watchful eyes. 'We shoved a hanky into the boy's mouth to shut him up,' the trafficker remembers, calmly plotting the strategy as if there was nothing abnormal in his actions, 'and we bundled him into a sack.' Another trafficker, who specialises in children, and is happy to appear on camera, says, 'I think there must be something wrong with treating children as goods, but I can't figure out what it is.' He likes to think of himself as an agent for parents who need to sell their children and a conduit for those who want to buy one. People do sell their children (if they don't have a birth permit, or are too poor to raise the child), but it is a murky world where a child becomes a missing piece in the commercial chain.

This particular trafficker admits that he used to sell women against their will, luring them first into a false sense of security by pretending to be a loving boyfriend. And although children are now much more lucrative, it is hard to understand why he wouldn't empathise with the families left behind: he has witnessed at first hand the devastation his older son feels since his younger brother went missing. The son, no more than 13, mourns the loss of a brother. 'I miss him,' he says. 'This year he would be nine...' The trafficker's son tries to articulate, pausing between thoughts and memories, shaking his head, and squeezing air out through tiny gaps in his mouth - small and potent sounds of regret that cannot be put into words. The twist, heartbreakingly, is that he later discovered that his own father was to blame for the disappearance. 'My grandmother told me my dad sold my brother,' he says. 'I thought my dad was very bad to do that. I felt very sad. At the time... at the time... I really hated him.'

As soon as the Chens discovered that Chen Jie was missing, they called 110, the emergency services. The police called back instantly for details and a description, but didn't come to their home. After a day of frantic searching, aided by neighbours with a car, the Chens went to the police station. A mix-up had occurred: because the emergency call happened late at night, the local police hadn't been passed the details. Looking around the train station and hotspots of trafficking didn't turn up any clues; they interviewed the neighbour, Zhang - nothing. By then, Chen Jie could have been halfway across China. Zhang has now moved to Mongolia, allowed to melt into another crowd in another country. Suspicion fell on another neighbour, Kong, for whom Lung used to be an apprentice. The Chens think he could have been in partnership with Zhang, picking Chen Jie as an easy target. The police questioned him for a whole day, but did not tell the Chens the result. Desperately, they have asked for Kong to be tested with a lie detector. There is a waiting list though - there are only a few in the whole country - and they don't know if they can afford it, or if it's even worth it.

They are encouraged, however, by a sliver of hope: Lung has heard breaking news that a ring of traffickers has been uncovered. The police have rescued around 40 babies, and families will be reunited with their kidnapped children - this is hope, in his eyes. 'We're both victims of the situation,' Lung says of himself and his wife, yet they are unwilling to criticise the government's policies: the police are working on their case, Lung says. Li comes on the line to explain that it's hard for the police, too: 'Police would go and try to investigate but even they get beaten up at remote townships...' Her equanimity crumbles later in the call, though, as she breaks down, admitting that she's not sure if she can keep living like this: the searching, the guilt, the dwindling figure of her husband, who has lost his appetite and is often unwell. Pregnant again, she worries that she won't know how to treat her new baby, that it will be unfair to Chen Jie to have another child. She doesn't sleep well, she says, dreaming every night of Chen Jie suffering in a poor village. And with a heart wrench Li realises that she has never dreamt he was bought by a rich family and living well, despite the plethora of news stories about children having a 'better life' with new parents. But she forces herself to keep going. 'I always remember what a father said who got his stolen boy back,' she says. 'He said as long as you keep your hope there is a chance; but if you give up hope and stop looking, the child is gone forever.'

Li's mother, the last to see Chen Jie, grief-stricken and carrying her own burden of guilt, often dreams of her missing grandson, too. The word in Chinese for dreaming and wishing is the same, and it is no surprise that her daytime longings spill into her night. 'I had a dream that my grandson came back,' she says. 'I held him in my arms and he asked me, "Grandma, are you tired?" I replied that I was not tired at all when holding my grandson. I was so happy that he finally came back.' And then, with sorrow, back to the terrible reality. 'Then,' she says, 'I woke up.'

Some names have been changed

· Dispatches Special: China's Stolen Children is on Channel 4 on 8 October at 9pm. To donate money to the Chens' search go to www.truevisiontv.com/china.htm