Vui also said the youth looked like ''caged animals'' at the facility.
The Samoa Observer newspaper reported the criticism was contained in an email to District, Supreme and Lands and Titles Court judges.
This followed a judicial visit of the facilities by Justice Vui, District Court Judge Talasa Lumepa Atoa Sa'aga and other officials earlier this month.
Vui said they were horrified to note the conditions in which children were being kept following a recent police decision to turn the Olomanu Rehab Facility at Mulifanua into a Prison farm manned by adult prisoners.
He wrote he believed the decision also had the blessing of the Minister of Police and possibly the Cabinet.
Justice Vui told members of the judiciary that the children were kept in heavily barred cells and slept on the concrete floor without mats or blankets.
"At this time of year at that attitude is criminal," he said.
"We saw one sheet being shared by a cell of six boys, wet washing dripping onto their floor as there is nowhere else to hang it because they are not allowed out of their cells at any time."
Justice Vui said the juveniles "looked like caged animals which are about what they are at present, a far cry from the open roomy conditions of Olomanu now being enjoyed by the adults."
Olomanu Juvenile Detention Centre was set up to separate young offenders from hardened adult prisoners.
Minister of Police, Tialavea Tionisio Hunt, declined to comment saying he was waiting on the Police Commissioner and his management to look into the allegations.