A database which holds the details of every child in the UK has become operational.
ContactPoint holds the name, ages, address and other information for an estimated 11 million youngsters in England for access by childcare professionals.
The £224 million system was set up following the death of Victoria Climbie, who was abused by her great aunt and her boyfriend, but has been hit by a series of delays and fears over security.
Technicians will start training around 800 practitioners including social workers, police and health care professionals to use the database.
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The pilot users are based in 17 local authorities in the north west of England and national voluntary sector partners, the charities Barnardo's and Kids.
More than 51,000 children deemed vulnerable have had their identities and information shielded, the Government said, after fears were raised about unauthorised access to data.
