London's Metropolitan Police stole the identities of some 80 dead children and issued false documents in their names for use by undercover officers, AFP reports citing Britain's Guardian newspaper.
The force authorised the practice over three decades for officers attempting to infiltrate protest groups, without informing the children's parents, the broadsheet said.
Its investigation described officers creating aliases based on the dead children's details and being issued with documents such as passports and driving licences in their names.
Some officers reportedly spent up to a decade pretending to be these people.
One unnamed officer, who adopted the fake identity of Pete Black while operating undercover in anti-racist groups, told the newspaper he felt he was stomping on the grave" of the four-year-old boy whose identity he used.
Another argued that the practice could be justified on the grounds that it was for the "greater good".