A child was taken away from her grandparents and put into foster care after they locked her in her room overnight.
The seven-year-old, from the West Midlands, was put into the care of the local authority after social workers found out that she had been locked in to prevent her from wandering around.
The couple say that Judge Rosalind Bush, a senior family court judge, ruled that the child should go into care after a private hearing in Wolverhampton.
But they have not had a written explanation or seen a judgment so don't know why the decision was made.
The child was locked in her bedroom at night on two occasions after she started to wander.
The grandparents said this was for her own safety, but social workers intervened.
The case was heard at a private family court hearing, but no ruling was ever published.
If the judge doesn't have a proper explanation as to why they're taking the child into care, then they shouldn't be taking the child into care
John Hemming, a former Liberal Democrat MP who campaigns for transparency in the justice system, said that the judge had to "show her working".
"To not give a reason just isn't acceptable. If the judge doesn't have a proper explanation as to why they're taking the child into care, then they shouldn't be taking the child into care," he said.
"I doubt she's the first child to have been locked in a bedroom," he added.
Legal advisers for the couple said they had asked the Court of Appeal to re-open the case.
Earlier this month researchers said people were being left with a "patchy understanding" of the family justice system because judges did not consistently following guidance on the publication of case rulings.
Academics at Cardiff University's School of Law and Politics analysed more than 800 rulings published in the two years after guidance was issued following complaints about court secrecy.
A report said "only 27 judges and 12 courts" had sent more than 10 cases to the British and Irish Legal Information Institute website for publication during that period.