New teams are being set up at airports and ports to save children being trafficked for sex or forced labour.
Children are used by traffickers as a commodity
The move by the Metropolitan Police follows a unique study - Operation Paladin Child - into the migration of children through Heathrow airport.
The Ports Safeguarding Team will operate at Heathrow, Waterloo Eurostar, and Croydon's asylum screening centre.
The multi-agency study at Heathrow found a small minority were at risk, but found no large-scale trafficking.
A separate report by a children's charity is expected to urge increased awareness among social services teams to spot the signs of trafficking.
End Child Prostitution, Child Pornography and the Trafficking of Children for Sexual Purposes (Ecpat UK) is expected to say the majority of social workers in London are not being given the right information and training.
The Heathrow study was carried out between August and November last year for non-EU unaccompanied under 18-year-olds entering the UK.
It identified 1,738 children travelling unaccompanied but the vast majority were
One of the recommendations expected is the deployment of teams of social workers and police to ports and airport, to look out for vulnerable children.
An Ecpat spokeswoman said the study was useful but more needs to be done.
She said: "They might come in as accompanied with adults purporting to be their parents
who are actually not related and they also come in as asylum seekers and EU."
One girl was 15 when she arrived from the Republic ofCongo before being raped and prostituted. She was eventually rescued by Customs.
She said those responsible came from her own country and some were English: "I'm scared to say the names of the people (and) later on they can find me.
"When I came here they always told us 'If you say my name, I've friends around the world who will find you and will kill you.'
"Why am I going to say the name when they say they're going to kill me and there's not enough protection?"
Angela Travis from Unicef said: "This activity by its nature is hidden from view. You won't see children being exploited on a street corner or private shop."
She said social workers need better training and there needs to be more safe and secure accommodation to house youngsters after they speak to police.
"It's about immigration, police and social services working together and that really needs to come with national leadership," she said.