About seven in 10 of the potential trafficking victims were girls
Up to 325 children a year are being smuggled into or around the UK to be used for slavery, crime or prostitution, according to research.
The Child Exploitation and Online Protection Centre (Ceop) identified 325 potential victims of child trafficking between March 2007 and February 2008.
Half were found to be working as prostitutes while others were involved in forced labour and drug smuggling.
Ceop's Jim Gamble said the true scale of the problem could be much worse.
The sophisticated methods used by traffickers and the fear felt by the victims meant many cases went unreported, the chief executive said.
Researchers from Ceop said 53% of the children whose age could be determined, were under 16.
They came from 52 different countries, including China, Afghanistan, Nigeria, Romania and Vietnam.
Some children were found working as forced labour in restaurants, on building sites and in beauty salons, or in private homes as domestic servants.
Others were drawn into street crime or coerced into working in cannabis factories.
Investigators also uncovered evidence of British children being trafficked around the UK for sexual exploitation.
The traffickers ranged from individuals to well-organised international networks and some used safe houses in other countries for children being moved across large distances by land, sea or air.
Overall, Ceop said, the process of trafficking could take up to a year and victims themselves could be made to repay the cost of their travel - anything between £5,000 and £40,000.
Mr Gamble said: "A crime where the children themselves sometimes don't even realise they are victims is a complex crime to crack.
"Young victims are typically manipulated by and collaborate with the trafficker because they have been promised a better life and that in itself presents a massive challenge for all authorities.
"Add to that the cultural barriers of language, potential threat from the traffickers themselves or the very new and alien world that these young people are walking into and you can see why many children don't have the confidence to speak out."