The trafficking of human beings is a problem in every African country, says the United Nations Children's Fund (Unicef).
The trafficked children can face terrible physical and emotional abuse
The report, which covers 53 African nations, says children are the biggest victims in what is a very complex phenomenon.
It describes how they are forced into slavery, recruited as child soldiers or sold into prostitution.
In Africa, children are twice as likely to be trafficked as women.
The BBC's Imogen Foulkes in Geneva says the report found that 89% of the countries had trafficking to and from neighbouring countries, but 34% also had a human trade to Europe.
Poverty, traditional migration and conflict are blamed for the traffic.
The trade in people is frequently regional.
Of the countries surveyed, 26% said trafficking was taking place to the Middle East.
And the trade is often in both directions.
Nigeria, for example, has received trafficked people from 12 African countries, but trafficked Nigerians have been found in a dozen countries too.
Much of this trade in children often has the tacit collaboration of the victims' own families where it is seen not so much as criminal activity but as a way for a large family to boost its poor income.
Joseph's back bears the scars of his beatings
The story of Joseph in Benin is fairly typical.
When he was 13 years old, a stranger arranged with his parents for him to go to neighbouring Togo for a better life.
However, he was put to work from 0500 to 2300 each day as a domestic help and was regularly beaten.
It took him three years of saving money to be able to phone home and be rescued by an uncle. Now 16 years old, he is back in school.
"I was so happy to see my little brother again when I returned home to Benin," he says.
The report's director, Andrea Rossi, says trafficking is a complex issue with many causes.
"Trafficking can start as slavery, children and women are sold, but it can also start as a migration process where children want to move.
"The only way they have to move - because for example it's illegal, because you cannot move, or it's difficult - the only option they have is to go through trafficking patterns."
There are no reliable figures for just how many people are trafficked in Africa, but it is likely to run into the millions.
Unicef is presenting its report to a meeting of African ministers in Benin.
The hope is to adopt an action plan to combat trafficking, one which will place the rights of the child at the centre of all future policy.