Mabondeli fiddles with her skirt as she tells the story of how her aunt accused her of being a witch when she was a small girl.

She was being taken care of by her grandfather after her parents were killed in a car accident. Her mother's sister believed Mabondeli was responsible for their deaths, saying she was a witch. "Because you have killed my sister you are a witch," she said. "Why are you staying here?"

Mabondeli, 12, wearing bright red flip-flops with a rose motif, cannot quite remember how she ended up on the street. She thinks she ran away to the market, where street children seek refuge. Mama Rose, who runs a centre that has taken in five children accused of witchcraft, tells a different version. She says neighbours had alerted her to the plight of a girl who was about to drown after being placed in a hole that was filling with rainwater.

"People came to tell me about a small girl who was about to die as the water was coming up to her neck," says Mama Rose, an energetic social activist.

Mabondeli now lives in what is effectively a school and orphanage run by Mama Rose. There is a classroom with two large rectangular blackboards at either end. Several rooms surround a small, sandy courtyard containing a slide, some swings and two leafy trees. Mabondeli and her fellow "witches", including a 22-year-old woman and a 16-year-old boy, live in spartan but clean rooms that have a bed – without mattress – and little else. Mabondeli says she never leaves the building.

In one sense, Mabondeli is lucky. She has a roof over her head and is receiving an education along with the other children who come during the day for lessons. She could be living on the streets of Kinshasa, a fast-growing city of 9.5 million people where wide new boulevards coexist with potholed dirt roads lined by brightly daubed breeze-block shops.

According to a report on street children (pdf) by the NGO World Vision – which is supporting Mama Rose's foundation, Esango, (meaning joy in Lingala) – the Democratic Republic of the Congo has experienced a marked increase in the number of street children and street gangs, a development that owes much to the country's rapid urbanisation. The highest concentration of street children is in Kinshasa.

In the 1990s, the number of street children was estimated at 35,000. The figure is likely to be dramatically higher today. Unsurprisingly, family poverty – Congo ranks last in the UN's human development index – is the leading cause of children ending up on the street.

Vianney Dong, assistant director of advocacy and communications at World Vision in Kinshasa, says impoverished families often see accusations of witchcraft directed at children as a pretext to abandon them.

"Witchcraft is an excuse to marginalise certain children," said Dong. "There are even supposed to be telltale signs of witchcraft – a child who eats too much but is not growing because the food is being eaten by a witch, or bedwetting. Or a child is blamed because the family business is not doing well, the child is seen as hindering the family's progress."

As a report by Unicef, the UN children's agency, pointed out, belief in witchcraft is widespread in Africa and other parts of the world. Allegations levelled at children are relatively new, however.

"Particularly in several central African countries, there are now alarming numbers of killings of adults accused of being 'sorcerers', and a growing and recent phenomenon in urban areas of witchcraft accusations against children and adolescents," said Unicef.

The report said becoming an orphan and being brought up by relatives is a risk factor, as is the arrival of a step-parent. Aggressive behaviour or a solitary temperament can leave children vulnerable to accusations of witchcraft, as can physical deformities or conditions such as autism.

Dong said church pastors can play a key role in combating the rise in accusations of witchcraft against children. Christian preachers, particularly from Charismatic and Pentecostal churches, have reinforced popular superstitions while whipping up emotions and turning the suffering of children into a lucrative business through exorcisms. For a start, says Dong, pastors have to be made aware that accusing children of witchcraft is against child protection law in Congo. Some have gone to jail in cases where a child has died after exorcism.

Some people in the country feel the problem is insignificant and overblown. But World Vision warns that the phenomenon of street children and gangs threatens to add another hurdle to peace and development efforts – especially attempts to create a safe social environment and equal opportunities for all – in a country already plagued by conflict.

"In Kinshasa, approximately 65% of criminal activity is claimed to be associated with street children and gang involvement. If this is true, and if this trend continues, Congo could be faced with a major crisis as more children and youth will be edged out of the family and community systems," it says.

Mabondeli has not had any contact with her family since she came to the centre 10 years ago. She says she likes it at Mama Rose's centre, but worries about her future because schooling is free only for the primary years. Maths is her favourite subject.

"I like it here, but I don't know exactly where I will go," she says, although she already knows what she wants to do in the future. "I want to be a doctor. I have diabetes and I know how to take care of it. I want to know how to take care of others."

• Mabondeli is a pseudonym