As the world marks the 200th anniversary of the end of the slave trade, Sarah Left says Ghanaian boys as young as four are still being sold as cheap labour

Kofi Azadavor is sitting stiffly on a bench under a mango tree on his family's compound, getting up every so often to tend the fire in the open-air kitchen. He looks smart in his school uniform of brown shorts and a blue-and-white checked shirt, but both school and family life are still fairly new experiences for the 10-year-old.

Kofi only returned home to his village near Sogakope, a small town in south-eastern Ghana, in June. When he was just four years old, his mother sent him and his older brother, Mawuta, to live with their uncle in a fishing town 250km away. It was the end of Kofi's childhood and the start of his life as a slave.

Kofi explains that while living with his uncle, he and Mawuta would get up very early in the morning, wash dishes and sweep the house, then head straight out onto Lake Volta to fish. They would spend the day casting out the heavy fishing net and checking for the catch.

When the net snagged on the branches and stumps at the bottom of the lake, Mawuta was made to dive into water to untangle it. It was a dangerous and delicate task, and the boys' risked drowning, contracting the disease bilharzia, and, if they damaged the net while setting it free, a beating from their master.

"My uncle would beat us sometimes," Kofi says. "If he said we should go to fish or farm and we said we were too tired, then he would beat us." When asked if he likes his uncle, Kofi just silently shakes his head.

This Sunday marks the 200th anniversary of the abolition of the Slave Trade Act, an event being commemorated in Ghana at Elmina castle, the country's most notorious slave trading fort, and in a series of events around the UK.

But across Ghana, and most stubbornly in fishing communities on Lake Volta, Ghanaian children are still being sold for as little as 200,000 cedis (£12) into a life of forced labour, malnutrition, physical abuse and no schooling.

Raymond Tchia was seven when his future master woke him from his bed and took him away to a life of fishing and diving into the deep water to untangle nets. Raymond lived in a one-room mud hut with 20 other boys and says they were fed only one meal a day. Now 17, Raymond was released only two months ago. He has never been to school before now.

"I did not enjoy living with that man. The man uses force. When I was young, I was very scared, so if I was to dive into the water and was afraid, he would beat me," Raymond says.

The International Organisation for Migration has rescued 612 trafficked children from Lake Volta since 2002, and it estimates that there are hundreds, and possibly thousands, more trafficked children still fishing on the lake.

Through a programme of community education and persuasion, IOM convinces fishermen to release trafficked children, and then reunites them with their families.

To secure their cooperation, IOM offers the fishermen help in improving their fishing business without relying on child labour, or help in setting up alternative businesses. The children's parents are offered micro-credit loans to help them keep the children at home, and the returned children are guaranteed school or vocational training.

Both parents and fishermen are also warned that Ghana passed a law against child trafficking in December 2005. Just last month, the country's authorities secured their first conviction under the new law.

Most of the children, mainly boys between the ages of 6 and 17, come from communities near Ghana's central and eastern coast, and are sent to live either with relatives who have migrated north onto the lake in search of better fishing, or with unrelated fishermen looking for cheap, obedient labour.

IOM project manager, Joseph Rispoli, says the trafficking of children to Lake Volta is a distortion of the much older practice of placement, where West African parents would send children to live with wealthier relatives to secure their education or training in a trade.

But the children doing the fishing almost never go to school, are generally fed only one meal a day, and are beaten on a regular basis, Mr Rispoli says. The work itself is dangerous as well as backbreaking, he adds.

"Sometimes it's just a bunch of eight-year-olds out on the lake alone in a rickety canoe with no supervision," he says.

Sharon Abbey, an assistant director at Ghana's department of social welfare, runs a shelter for trafficked children at Madina, just outside the capital, Accra.

After IOM and its partner NGOs rescue the children from the lake, they are sent to Ms Abbey's shelter for two to three months for counselling and an introduction to the classroom while their families are traced.

She introduces us to Joel Adinortey. He does not know how old he is, but she estimates he is about six. Joel cannot remember the name of the town he was in, and cannot yet speak about the experience.

"You wonder how a mother can take a child this young to be subjected to this. You wonder what sort of mother that is. When he came here, he was crying all the time," she says.

The children also have a hard time coming to terms with their parents' decision. Raymond Tchia says he thinks his father is dead, and he has no memory of his mother, not even a picture of her in his head. He is not angry with her for sending him away, he says, he feels nothing about her.

Kofi's mother, Favour Azadavor, insists she never received money from her brother for sending Kofi and Mawuta to him, only food parcels. In the six years they were away, she did not see them once.

Ms Azadavor, who scrapes a living as a subsistence farmer, has 10 surviving children and says she simply could not cope financially. "I sent the two because the father could not take care of them and, looking at the numbers, I could not afford to take care of them," she says.

The return of Kofi and Mawuta has clearly been less than a joyful occasion for Ms Azadavor. She says she was happy to have them back and regrets sending them away, but providing for them is still a worry now, despite IOM providing a school uniform, supplies and any fees.

"There has been no reduction in the suffering," she explains.

In Kofi's hometown of Sogakope, Julius Kwadzo Ameku runs a local NGO, Fysso, that has reunited 50 children with the parents who sold them or sent them away.

He says that some of the parents were angry with Fysso for returning their children without additional money (Fysso is just beginning to offer micro-credit and training to the parents of trafficked children).

"The parents say that if you brought them back, you must take care of them. They say, it is your duty because we did not ask you to bring them here."

Mr Ameku feels the solution lies in tackling three problems. The parents need education about child welfare, how to keep the children safe and the importance of sending them to school.

He points towards a group of children selling loaves of bread on the main road, in full view of police at a checkpoint. "It's not just about poverty. It's about mindset and attitude," he says. "The parents should be made to feel the full rigours of the law if the children are not in school."

Second, he says, much more work needs to be done to promote family planning. "People give birth to so many children and with that they have the problem of taking care of them. So to give them out is a relief. Those children work and the masters send the parents some money, and they use the money to take care of the remaining children."

Finally, there needs to be greater employment opportunities for the parents, so that they can afford to take care of their children at home.

Ms Abbey just hopes that the children passing through her shelter will be able to make something of their lives, and that they will find the self-confidence they need.

"They should not think that life is like that and that adults can always push you around. We are not all like that. They should know that they have rights," she says.