Many West African children are forced to work in near-slavery conditions when their parents have died, according to the New-York-based campaign group Human Rights Watch (HRW).
Some children have to make their own way home
A HRW report details cases of children as young as three - many of them orphans - who were made to work as domestic or agricultural labourers.
It describes children suffering physical and emotional abuse, and then being told to make their own way home - often from other countries.
"Orphans face many grave human rights abuses, and trafficking is surely one of the worst," said Jonathan Cohen, the author of the report.
"Trafficking in child labour occurs along numerous routes in West Africa, and governments aren't doing enough to stop it," he said.
The issue of child labour in West Africa made headlines last year following reports that almost half the chocolate produced in the United States came from cocoa beans harvested by young people in Ivory Coast.
'Tip of the iceberg'
Mr Cohen said the cocoa farms were "just the tip of the iceberg".
The report focuses on Togo, which it says suffers desperate poverty linked to the suspension of aid from Europe after an election 10 years ago was marred by irregularities.
Togolese boys told the organisation they ended up as agricultural labourers in Nigeria because they could not afford to pay school fees at home.
They said they were beaten if they complained of tiredness during 13-hour working days.
Girls who fled their traffickers often found themselves with nowhere to turn and ended up sleeping at churches or the homes of strangers - or being forced into prostitution in the Togolese capital Lome.
Togo has drafted a law prohibiting child trafficking and imposing fines of $1,500 to $15,000.
But the organisation charges that few people have been arrested under existing laws against kidnapping and procuring - and fewer still are prosecuted and jailed or fined.
It urges Togo to ratify international treaties banning child trafficking.
It also calls on neighbouring countries and on international organisations and donors to help fight the problem.