The use of dead children's identities by Scotland Yard undercover police officers was “common practice”, a chief constable investigating the matter has found.
In a letter to MPs, Mick Creedon, who is leading Operation Herne, said no families of children whose identities were used had been contacted and informed.
Mr Creedon, the Derbyshire Police chief who was brought in to take over the investigation from the Metropolitan Police in February, said: "This issue is very complicated and mistakes could put lives in jeopardy."
Herne was set up in October 2011 to look into allegations made against the Met's Special Demonstration Squad (SDS), including using dead children's identities and engaging in inappropriate sexual relationships.
Mr Creedon was responding to a series of questions put to him by the Home Affairs Select Committee.
Answering how many dead children's identities are estimated to have been used by undercover police, he said: "I am not able to answer this question at this time with any degree of absolute certainty but I can say that this was common practice within the SDS."
Mr Creedon confirmed that Scotland Yard has received a number of speculative inquiries from relatives asking the force to confirm that their dead child's identity was used.
He said: "No families of children whose identities have been used have been contacted and informed.
"No answer, either positive or negative, has yet been given in relation to these inquiries from families."
The chief constable said it would not be "appropriate" to provide details on the number of children the Meropolitan Police has identified as being born out of a relationship with undercover officers.