Legislation requiring local authorities to provide independent child trafficking advocates to all children who need them was among provisions in the Modern Slavery Act 2015.
A trial took place in 23 areas between September 2014 and September 2015, but in December 2015 the Home Office announced that the planned national launch would be delayed as there was "work still to be done" on the initiative.
Since then the scheme has only launched in three "early adopter" areas - Hampshire, Greater Manchester and Wales.
Speaking in a parliamentary debate yesterday Home Office minister Victoria Atkins said the Independent Child Trafficking Advocates Service, run in partnership with Barnardo's, will launch in the West Midlands next week.
The service will then be expanded to the East Midlands from January 2019, and in Croydon from April 2019. However, no details on a national launch have been given.
Victims of child trafficking can be subject to child sexual abuse and exploitation or criminal exploitation.
"These advocates provide invaluable specialist support to child victims of modern slavery," Atkins said.
"It is horrendous that victims of modern slavery have their freedom denied and that is why this government is absolutely determined to do all we can to tackle this crime."
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Meanwhile, Prime Minister Theresa May has announced a £5m fund to support "innovative ways" to improve the response to child trafficking.
Barnardo's chief executive Javed Khan said it is crucial all trafficked children get the help they need to recover from the trauma they have suffered.
"By developing [the independent advocates] service we will be able to support more children who are trafficked into the UK or from one part of the UK to another.
"We will also be able to upskill more professionals working with children to understand their vulnerabilities, including the risk of being trafficked internally.
It emerged in August that the three early adopter sites received a total of 215 referrals within the first year. The level of demand was so high that the Home Office funded the recruitment of two additional advocates to support the existing six advocates.