Thousands of people have attended a rally in Calcutta, India, to mark the start of a three-week march to Delhi to protest against child trafficking
The organisers are calling for the repatriation and rehabilitation of victims of child trafficking.
They want the Indian government to pass laws that prosecute those who supply children for forced labour and sex.
The marchers, including many children who have been trafficked, will also stop in Bangladesh and Nepal en route.
The march has been organised by the Save the Childhood Movement and the Global March Against Child Labour in India and is supported by several UN agencies.
Kailash Satyarthi, chairman of the Global March Against Child Labour, says South Asia is a major source, destination and transit area for child trafficking of all forms.
"Children are being taken for forced labour and bonded labour," he says.
"Children are being used for child marriages. Child prostitution is of course there, then a lot of children are taken as camel jockeys."
Some children, he says, are kidnapped and sold so their organs can be harvested for transplant operations.
One of the young marchers is a boy of 13 who says he was lured from his village in Bihar by a man with sweets, kidnapped, and taken to Punjab where he was made to work 12 hours a day, every day.
The organisers say one of the goals of the march is to publicise the issue.
"Trafficking of children for forced labour is a hidden issue, with the people in the rural areas still being ignorant and thus being vulnerable to being trafficked for forced labour," said Nandita Das, a film actor and social activist, at the media launch for the march on Friday.
Mr Satyarthi wants India to enact laws against child trafficking for forced labour.
Of the eight million children the International Labour Organisation estimates are involved in forced labour worldwide, more than a million have been trafficked, many of them in India.
Human Trafficking & Modern-day Slavery