Undercover police officers working for Britain's largest force used the identities of dead children and issued fake passports in their names, reports the Guardian.
The Metropolitan Police authorised the practice for covert officers infiltrating protest groups without consulting or informing the children's parents, the newspaper said.
Over three decades, generations of officers reportedly went through national birth and death records in search of suitable matches.
Officers were then given aliases and issued with official documents such as driving licences and national insurance numbers.
Last night, Scotland Yard said the practice was not "currently" authorised.
More top news
A woman who attempted to get her idol's full pout was left with hugely swollen lips when her plan went horribly wrong.
All would-be MPs should be forced to tell voters what paid jobs they have and whether they would keep them if elected, Lord Bew has said.
A Para who won the Victoria Cross gave up his military history studies just weeks into the course as he wanted to be a part of it instead.