(CNN) In Benin, when children fall sick, their parents often turn to voodoo. The West African nation is, after all, its spiritual home. Officially a state religion since 1996, Voodooism is practiced by 17% of the population, with many outside of the religion professing a cultural link to some of its rituals.
But what happens inside the hundreds of facilities dotting the country is a mystery to most outsiders. Now advocates are raising the alarm saying the facilities may harm the children they aim to help.
Djofin Assou Gilbert is an advocate for children in Benin. He first became concerned about the practices inside the convents in early 2015, when he noticed a group of children standing outside a convent.
"It was the middle of the day and the children weren't wearing their school uniform," he remembers. "I wanted to know why they weren't in school. I tried to ask a little girl why she was there, but she couldn't answer."
The girl, he says, had lost her mother tongue.
"I was desperate to find out more. Like many people in Benin I'd heard of these convents, but I didn't know what was happening inside."
"Those who practice Voodooism believe that illness is caused by evil spirits. If children fall sick, their parents seek treatment through Voodoo gods. The children allegedly possessed by spirits can be sent or even 'sold' to be healed in Voodoo convents," notes Hadrien Bonnaud, a communication specialist for UNICEF based in Benin.
The ceremonies that are meant to heal these children are expensive: about $1800 (a princely sum for a population that lives on less than $1 per day). In order to afford treatment, UNICEF says some parents sell their children to work in the convents until the debt is paid off (a practice that can take months or even years).
"If they are unable to pay their debts, the children are forcibly taken from them," explains Bonnaud.
UNICEF is one of several NGOs that have become concerned in recent years with the practices carried out inside Benin's traditional Voodoo convents. The exact number of convents in the country is unknown, but as of 2014, UNICEF has identified 432 in five out of Benin's 77 municipalities.
Plan International, a children's rights advocacy group, has also done research on the conditions inside the convents. Operating in the district of Couffo in south Benin, the organization has interviewed dozens of parents, voodoo priests and children about life inside these spaces.
"I was given a concoction and every time I took it, I was sick -- that was my treatment until I healed," recalls Houndedji, 6, one of the children Plan International interviewed.
In some cases a voodoo god will be assigned to a child, and symbolic scars will be carved into the skin. Madeline, 10, another child that Plan International interviewed, recalls the scarification she received as part of her treatment.
"It was very painful and there was so much blood... it was everywhere."
According to the charity, children as young as two years old can be kept in these convents -- where access to education and healthcare is minimal. These children have to give up their names, learn a new language (that of voodoo) and begin an entirely new life. In some instances, when the initiated are finally released (sometimes up to a decade after they arrived), they no longer have families to return to.
"Seven years is far too long to be kept in a convent," argues Angela Singh, a global press officer at Plan International.
"They come out and many of them have grown up; sometimes their parents have died, they have nowhere to go, no education. It's difficult to integrate back into communities. Their childhood has just passed them by."
Further complicating matters is the fact that only those initiated into the voodoo religion are allowed entry to the convents, making it hard both to monitor conditions inside and provide those living in the convents with the medical attention they might need.
"Very often convents are places kept in secret and the initiated who attend them have to keep those secrets," says Bonnaud.
After Gilbert saw the children in 2015 and grew concerned, he arranged meetings with chief priests and then their president, Mama Hounza Tognon Mahouchi.
"We discussed the situation and he agreed with my ideas. However, he put in place a condition that I needed to get indoctrinated into voodooism, to bring about reform." Though he can't discuss the rituals he had to undertake, he was subject to scarification on the side of his body.
Once initiated, Gilbert had open access to the convents and could speak more candidly with its priests. Gilbert works with ReSPESD, a child advocacy group that partners with Plan international. He notified Plan International Benin of his findings.
Both Plan International and UNICEF have been holding talks with community leaders to limit the confinement period spent inside these convents and provide the children inside with greater access to education. In 2015, both organizations met with voodoo chiefs, local authorities and political figures to raise awareness about child rights within the convents.
In Couffo alone, 310 children (193 girls, 117 boys) left compounds. Some had homes to go to while others fell under the responsibility of Gilbert, who runs an orphanage. Of those released, 280 are now in school and 30 have gone into apprenticeships.
Houndedji and Madeline both aspire to be a headmistress one day, a future once unimaginable in the convent. Eric, who still doesn't know where his parents are or what happened to them, has loftier ambitions: he wants to become president of Benin.
Singh is quick to stress that throughout discussions, the finger of blame was not pointed at the priests.
"They believe they are doing what's best for the child," she says. "These priests were willing to look at different ways to adapt their practices so children can get an education."
"I let this go on because I was ignorant," chief priest Mahouchi told Plan International. "I believed it was our laws and regulations, governed by the voodoo and the oracles that determined how long children should spend in the convent."