A Mexican shelter handed children in its temporary care to a religious sect, which then adopted them through a legally dubious process, Mexican authorities have said.

Prosecutors announced on Tuesday that three more of the children had been found, bringing the total to 12 out of the 15 children who went missing from the Casitas del Sur shelter.

Today, the staffing and the procedures for the care of children in the government's temporary shelters continue to create conditions that make another Casitas del Sur case possible. Margarita Griesbach, child rights activist and lawyer

The three newly found people showed up last week at prosecutors' offices in Puebla state, near Mexico City, and identified themselves as children taken from the shelter, though two are now adults, according to a federal official.

Like many of the other recovered children, they had been given to members of the evangelical sect, called the Restored Christian Church, through an adoption process of questionable legality.

Religion expert Bernardo Barranco said the religious sect took advantage of the Mexican government's lack of adequate shelters for at-risk youth by offering its services under the guise of a philanthropic effort.

"The Casitas del Sur were just a facade for an ambitious indoctrination project ... to take children who were defenceless, trusting, blank slates, who would believe everything the sect told them," Barranco said.

The shelter housed children from broken families or whose parents were temporarily unable to care for them.

But by the time some relatives came back for their children, they had disappeared.

Change needed

The shelter was raided by police in 2008 and dozens of children were removed from it, but some remained missing.

Several arrests have been made in the case, but there have been few convictions.

"The authorities bear a lot of the responsibility for all of this" because they sometimes entrusted children to the groups without following proper legal procedure, and without having checked out the shelter enough, said Margarita Griesbach, a child rights activist and lawyer.

"Today, the staffing and the procedures for the care of children in the government's temporary shelters continue to create conditions that make another Casitas del Sur case possible," Griesbach added.

The church had previously denied any involvement in the disappearances.

Prosecutors found the first of the missing children in 2009.