Jeff and Jennifer Bramley,disappeared from their Cambridgeshire home in September with five-year-old Jade Bennett and her half sister, three- year-old Hannah on the day they were due to hand back the children to social services. The handwritten letter, sent to newspapers and a television station, marks the first time they have made contact for 17 weeks. They ask police and social services to let them live together as a family.
Although the letter, which had a Nottingham postmark, was unsigned, police are taking it seriously because it contains information that only the Bramleys could know.
The couple wrote: "We Jeff, Jenny, Jade and Hannah write this letter to tell the plight of a family that love each other and wishes to stay together. Jade and Hannah were told about us and told we would be their forever Mummy and Daddy.
"After we had met the girls several times in their foster home, they came to live with us. They soon grew to love us as their Mummy and Daddy, as we grew to love them as our daughters. Jade and Hannah were looking forward to their new lives with us."
The Bramleys said they were good, honest, caring people who were willing to give up their home, friends and jobs to keep the girls "with the parents they love and desperately want to share their lives with.
"We were approved to be Jade and Hannah's new Mummy and Daddy, they were placed with us for us to adopt ... it is misleading to call us foster parents. Social services seemed pleased with us and told us everything was fine until one day they said we were too safety conscious by saying `no' and `don't' too often to the girls.
"The children have been told that they are to move on to another forever Mummy and Daddy.
"Jade and Hannah have cried saying they love us and don't want to live with anyone else and that if anyone comes to take them away they will hold on to us, not letting go." The letter ends with an appeal asking for help to adopt the girls.
"Jade and Hannah are two bright, intelligent, articulate children who love us with all their hearts. We ask therefore, will someone help us to be legally their Mummy and Daddy for ever, making the hopes and dreams of these two wonderful girls come true."
A spokesman for Cambridgeshire Police said that although the letter was unsigned, he believed it was "likely" to have been written by the Bramleys. "It is a major breakthrough and we are delighted they have chosen to make contact," he said. "It is obviously not in the long-term interests of Jade and Hannah to stay away from home."
When Mr Bramley applied to become a foster parent, he did not disclose to social workers that he had been in foster care himself as a child. A Cambridgeshire County Council spokesman said that would not automatically have disqualified him from fostering children.
The couple had pounds 5,000 with them when they left and have not withdrawn any money since.