The database was proposed after the death of Victoria Climbie
A controversial database which holds the details of every child in England has become available to childcare professionals for the first time.
ContactPoint, a response to Lord Laming's report following the death of Victoria Climbie, is beginning its national roll-out in the north west.
But the system, costing £224m, has been delayed twice amid data security fears.
The government says it will enable more co-ordinated services for children and ensure none slips through the net.
It will hold the details of 11 million children and young people aged up to 18 years.
The delays were prompted by concerns over access to the database. In 2007, a report into the project by auditors Deloitte and Touche said it could never be totally secure.
Last summer ministers delayed the database, admitting there were some "issues" identified in testing.
It says 390,000 people will have access to the database, but will have gone through stringent security training.
The system will be available to workers in 17 local authorities in the north west of England, before eventually being rolled out across the rest of the country.
More than 51,000 children deemed vulnerable will have their identities and information shielded, the government says, after fears were raised that information about children's whereabouts could fall into the wrong hands.
Name, address, date of birth, gender and contact details for parents or carers
Each child also has a unique identifying number
Details of the child's school and GP practice and for other practitioners or services working with the child
Whether the practitioner is the lead professional for that child
The government said the database was vital to prevent any child slipping through the net, and would enable professionals to see quickly and easily which other services and people were in contact with a child.
England's children's minister, Delyth Morgan, said: "Under current arrangements if a practitioner believes that a child is at risk or may need additional support, for example if they have a disability, they may have no way of knowing whether other services might already be in contact with that child.
"We estimate that ContactPoint, when fully operational, can save at least five million hours of professionals' time, freeing them up from trying to track down other practitioners and enabling them to spend more time on the child."
The Conservatives have called for the database to be scrapped.
But it has been welcomed by the chief executive of children's charity Barnardo's, Martin Narey, who said it "would make it easier to deliver better-co-ordinated services".