If you believe in traditional Christianity, you need, necessarily, to believe in spirits, both good and bad. The church I grew up in believed in these things, and exorcisms, as well.

The way I was taught exorcisms were practiced was simply through prayer. I was taught that all you had to do was command it in the name of Christ, and an evil spirit had to obey that. There's a scriptural basis for that.

However, I see children as essentially innocent and I can't imagine believing a child to be possessed by a demon. These people are obviously not mentally well, and did a very evil thing, but I don't think it's fair to blame it on the Christian faith.