A High Court judge has asked a council boss for an explanation after complaining of "lackadaisical" efforts by social workers.
Mr Justice MacDonald said social services staff at Cheshire East Borough Council had been asked to assess people who might be able to care for a vulnerable 11-month-old girl.
The judge said assessments contained "patent defects" caused by social work which was at best lackadaisical and at worst in contravention of statutory guidance.
He has ordered Nigel Moorhouse, the council's head of service for children's social care, to explain "regrettable mistakes".
Mr Justice MacDonald has outlined complaints in a ruling after analysing the toddler's case at a private family court hearing in Liverpool.
He said there had been a failure to comply with professional obligations.
The judge named two social workers who he said had carried out "inadequate and fundamentally flawed" assessments.
He said: "The serious mistakes made by Cheshire East Borough Council in this case are of very real concern and must not be repeated."
Mr Justice MacDonald said the toddler's mother and father were unable to look after her and social workers had been asked to assess a number of relatives as potential carers.
The judge said the little girl and family members could not be identified.
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