A heroin addict is thought to have "spirited" two of her three children to Bangladesh after social workers raised welfare concerns, the High Court has heard.
Shahera Khatun and her daughters Azima Ali, nine, and Samira Ali, three, vanished from their home in London earlier this month, judge Mr Justice Cobb has been told.
Detail of the case emerged at a hearing in the Family Division of the High Court in London. Mr Justice Cobb said family members and the London Borough of Tower Hamlets - the local authority involved - could be identified.
The children's father, Imran Ali, 38, has been given a four-month jail term after the judge decided he had not revealed all he knew about the children's disappearance.
Lawyers for Tower Hamlets told the judge that Ms Khatun, who has relatives in Scunthorpe, Lincolnshire, was a heroin addict.
And they said messages found on a mobile phone belonging to Mr Ali pointed to her being in Bangladesh with the children.
"It is a deeply troubling story," said Mr Justice Cobb, as he jailed Mr Ali.
"These two little children have been, it appears, spirited away from this country to Bangladesh."
The judge concluded that Mr Ali was in breach of a court order requiring him to give any information he had about the children's whereabouts to the authorities.
Mr Ali denied breaching the order and being in contempt of court.
He told the judge: "I believe that I don't deserve this punishment."
The couple have a third daughter, who will celebrate her first birthday in the next few weeks, said lawyers. She is in interim council care but has had contact with her mother.
Azima and Samira lived at home but social workers were supervising their care.