Cheshire police launched the inquiry after complaints against the former housewarden of Greystone Heath community boys' home in Penketh, Warrington, and it has since spread to include other homes in Cheshire and Merseyside.
Alan Langshaw, 42, from Moreton, Wirral, was jailed for 10 years last month for sexual offences against boys aged between 10 and 20, committed between 1977 and 1994.
The offences took place while he was working at Greystone Heath, and later at St Vincent's Community Home in Formby, Merseyside, and at Halton College, Widnes.
Police confirmed that after Langshaw's case came to light they launched an investigation last April into a number of allegations by boys at other homes in Cheshire and Merseyside. The inquiry had been kept secret until a BBC regional television programmedisclosed its existence yesterday.
The three Cheshire homes involved in the inquiry are Greystone Heath, St Aiden's Assisted Community Home in Widnes and Danesford Children's Home in Congleton. All three homes closed a number of years ago for reasons not linked to the investigation.
On Merseyside, the homes involved are St Vincent's and Dyson Hall in Fazakerley, Liverpool.
Police in Cheshire have charged four other men with sex offences and all are currently awaiting crown court trial.
Two men have been charged with offences by Merseyside police and both face committal proceedings later this month.
Cheshire and Liverpool social services departments are also involved in the investigation, which is based in Warrington. The case is proving so complex that the police computer system, known as Holmes -which is normally reserved for major murder investigations - is being used.
"The sensitive nature of the inquiries being undertaken, the number of ex-residents involved, and the historical nature dictate that this investigation will take a considerable time to complete to ensure that the issues involved are fully and thoroughly investigated," a police spokesman said.
The British Association of Social Workers, which represents about 10,000 social workers, said any breaches of its strict ethical code by its members would result in disciplinary action.
In a statement, the association also called on the Government to set up a social work council to regulate standards of behaviour in the profession, and to establish a national register of paedophiles to help prevent child abuse.
The statement added: "Child sexual abuse is a major problem in this country and every effort must be made to deal with the problem, whatever the background or profession of the abuser."Reuse content