Jeff and Jenny Bramley disappeared from their home in Cambridgeshire last September, hours after they were due to return the two little girls to social services.
They reappeared last January and after a private hearing in the High Court, a judge ruled that it was in the interests of Jade Bennett, five, and her half-sister Hannah, three, that the Bramleys be granted temporary custody.
But to the surprise of many of those close to the case, Cambridgeshire police issued a statement yesterday, saying: "A married couple, aged 35, are to be charged with child abduction, the Crown Prosecution Service has advised.
"The couple were interviewed by police officers in January and a file was submitted to the CPS for review and advice."
The couple will appear in court on a date to be fixed. Cambridgeshire social services declined to comment.
But a police source close to the case admitted there was "great surprise" that the CPS had decided to proceed with the case. Abduction carries a maximum seven-year sentence.
A spokesman for the National Association of Probation Officers said that the case was "unique".
The Bramleys disappeared after social services refused them permission to adopt the girls they had been fostering for seven months with a view to keeping them permanently.
They returned only after an open letter from Cambridgeshire social services stated that the department would not oppose them reapplying to adopt the children.
The couple wrote an open letter to several newspapers, pleading to be allowed to be the girls' "Mummy and Daddy forever".
At a private hearing in the Family Division of the High Court in January, Mrs Justice Hogg said the children could stay with the Bramleys for the time being.