I thought this Guardian article concerning the "toxic" role of Christian belief in current African (principally Congolese) beliefs about witchcraft. It would seem that particular (and thus significant to these cases of violence against children so 'possessed') aspects of African folk belief about witchcraft concerning "possession by spirits", were actually imported from Western Pentecostal missionaries:

"In their present form, beliefs in witchcraft are not "traditional" – changes since earlier times are obvious. Modern beliefs see the power of witchcraft as emanating from evil spirits that possess the witch and endow him or her with the power to harm. This belief in possession by evil spirits has been promulgated in Africa by western missionaries of fundamentalist, particularly Pentecostal, Christian beliefs."

Furthermore, belief in the possession of *children* in particular by evil spirits also represents a recent change from traditional African folk beliefs about witchcraft.

"A recent change is the accusation of children, who may be singled out by parents or other caretaking adults for a variety of reasons that distinguish them from among others in the household: bad dreams, bed-wetting, children who are cleverer or stupider, who have different likes and dislikes – almost anything can be the symptom of a possessing evil spirit. Often, the accused are outsiders – either stepchildren or refugees in the chaotic postwar Congolese state; trafficked children or child soldiers"

http://www.guardian.co.uk/commentisfree/belief/2012/mar/01/witchcraft-curse-africa-kristy-bamu