They came from across China to protest under the watchful gaze of the police, brandishing handmade placards with pictures of their missing children. In a sign of growing discontent, the parents' rare demonstration in the centre of Beijing was aimed at pressuring the authorities to do more to investigate the cases of tens of thousands of children snatched and sold every year.
"My wife and I can't sit at home waiting for the police, we keep looking. The longer you wait, the more hopeless you get," said the father of one boy Liu Jingjun, who went missing this year.
Many of China's missing boys are sold to childless couples who turn to criminal gangs to supply the treasured male heir while the girls are trafficked to become prostitutes or brides in rural areas. China's One Child Policy has led to an alarming shift in the gender divide with a major shortage of girls.
Baby boys can sell for as much as £4,000, while girls are sometimes sold for just £300, according to some child welfare groups. Some end up working in brick kilns in the heartland, others as beggars in the booming cities of the east coast. Scandals have occasionally erupted over the sale of abducted children to orphanages for adoption abroad.
The parents protesting in Beijing met through a website called "Baby Come Home" which lists more than 2,000 missing children and led to an informal network of desperate adults. Some were reluctant to give their names in Beijing because of the police presence and many returned home after authorities told them to end the protest.
The authorities responded to the problem in April last year with a high-profile public crackdown on trafficking. Officials say this has led to the break-up of nearly 2,400 criminal gangs and seen nearly 16,000 people detained.
But the US State Department's trafficking report for 2010 said that despite significant efforts, the government did not comply with the "minimum standards" for eliminating trafficking. It said there were continued reports of children being forced into prostitution.
China does not give figures, but an estimate based on reports for a British television documentary suggested that up to 70,000 children were snatched from the streets every year in China.
In a country where the social welfare net is still being constructed, having a child provides security in old age. A preference for males is common in China's rural regions, and families sometimes abort baby girls because they are limited to one or two children by family-planning laws.
But this preference has caused a potentially disastrous gender imbalance in the world's most populous country. In some regions, the male-female ratio can be as high as 130 males for every 100 females, compared to an average ratio of 107-to-100 in industrialised countries.
Daughters become members of their husband's family when they marry and move away, prompting the saying: "Raising a daughter is like watering someone else's fields", whereas boys grow into men who can till the fields and work as migrant labourers in the cities.
The gender gap has created a situation where there are not enough women of marrying-age for China's single men – and organised gangs have moved in to fill the gap.
Police say they have freed more than 10,000 abducted women including 1,100 foreigners, mostly from Vietnam, Cambodia, Laos and Mongolia, since April last year as the widening gender gap fuels bride trafficking and prostitution.
One mother from Datong in Shanxi province lost her daughter Wang Min back in 1997 and has been searching for her ever since. "My daughter was only eight when she disappeared, she'd be 21 now," says her mother, her voice cracking as she spoke. "I went to the police immediately after she disappeared, but since I cannot provide any evidence to the police, they cannot really give any practical help. All I can do is travel to places when I hear of a clue.
"I have another child now, but I still miss Wang Min, I miss her a lot. Maybe I won't even recognise her now if she passed me in the street, but I will never give up hope of finding her," she said.
Li Ni's son disappeared in February 2009 in Xi'an. "A lot of parents have already travelled to nearly all the provinces in China, using all the money in the family," she said.
"I am so desperate to find my son and I will continue to look for him using whatever means necessary, no matter how long it takes, no matter how many hardships I have to endure."
"I believe those who abducted our kids, they are still human beings, they still have feelings just like you or me. I know of one kidnapper who took a kid for a long time, then saw the pain he was causing the parents on the media, so he brought him back because of the pressure from his heart," she said.
"Maybe one day my son will also come back to me in this way, and I will fight for him until that day."