The rainy season is over and the Niger Delta is lush and humid. This southern edge of West Africa, where Nigeria's wealth pumps out of oil and gas fields to bypass millions of its poorest people, is a restless place. In the small delta state of Akwa Ibom, the tension and the poverty has delivered an opportunity for a new and terrible phenomenon that is leading to the abuse and the murder of hundreds, perhaps thousands, of children. And it is being done in the name of Christianity.

Almost everyone goes to church here. Driving through the town of Esit Eket, the rust-streaked signs, tarpaulins hung between trees and posters on boulders, advertise a church for every third or fourth house along the road. Such names as New Testament Assembly, Church of God Mission, Mount Zion Gospel, Glory of God, Brotherhood of the Cross, Redeemed, Apostalistic. Behind the smartly painted doors pastors make a living by "deliverances" -- exorcisms -- for people beset by witchcraft, something seen to cause anything from divorce, disease, accidents or job losses. With so many churches it's a competitive market, but by local standards a lucrative one.

But an exploitative situation has now grown into something much more sinister as preachers are turning their attentions to children -- naming them as witches. In a maddened state of terror, parents and whole villages turn on the child. They are burnt, poisoned, slashed, chained to trees, buried alive or simply beaten and chased off into the bush.

Mary Sudnad (10) grimaces as her hair is pulled into corn rows by Agnes (11) but the scalp just above her forehead is bald and blistered. Mary tells her story fast, in staccato, staring fixedly at the ground.

"My youngest brother died. The pastor told my mother it was because I was a witch. Three men came to my house. I didn't know these men. My mother left the house. Left these men. They beat me." She pushes her fists under her chin to show how her father lay, stretched out on his stomach on the floor of their hut, watching. After the beating there was a trip to the church for "a deliverance".

A day later there was a walk in the bush with her mother. They picked poisonous "asiri" berries that were made into a draught and forced down Mary's throat. If that didn't kill her, her mother warned her, then it would be a barbed-wire hanging. Finally her mother threw boiling water and caustic soda over her head and body, and her father dumped his screaming daughter in a field. Drifting in and out of consciousness, she stayed near the house for a long time before finally slinking off into the bush. Mary was seven. She says she still doesn't feel safe. She says: "My mother doesn't love me." And, finally, a tear streaks down her beautiful face.

Nwaeka is about 16. She sits by herself in the mud, her eyes rolling, scratching at her stick-thin arms. The other children are surprisingly patient with her. The wound on her head where a nail was driven in looks to be healing well. Nine- year-old Etido had nails, too, five of them across the crown of his downy head. Its hard to tell what damage has been done. Udo, now 12, was beaten and abandoned by his mother. He nearly lost his arm after villagers, finding him foraging for food by the roadside, saw him as a witch and hacked at him with machetes.

There are sibling groups such as Prince, four, and Rita, nine. Rita told her mum she had dreamt of a lovely party where there was lots to eat and to drink. The belief is that a witch flies away to the coven at night while the body sleeps, so Rita's sweet dream was proof enough: she was a witch and because she had shared food with her sibling -- the way witchcraft is spread -- both were abandoned. Victoria, cheeky and funny, aged four, and her seven-year-old sister Helen, a serene little girl. Left by their parents in the shell of an old shack, the girls didn't dare move from where they had been abandoned and ate leaves and grass.

Pastor Joe Ita is the preacher at Liberty Gospel Church in nearby Eket. "We base our faith on the Bible, we are led by the holy spirit and we have a programme of exposing false religion and sorcery." Soft of voice and in his smart suit and tie, his church is being painted and he apologises for having to sit outside near his shiny new Audi to talk. There are nearly 60 branches of Liberty Gospel across the Niger Delta. It was started by a local woman, mother-of-two Helen Ukpabio, whose luxurious house and expensive white Humvee are much admired in the city of Calabar where she now lives. Many people in this area credit the popular evangelical DVDs she produces and stars in with helping to spread the child witch belief.

Sometimes I think the only cure for the sickness that is Africa is a big nuke.