Spiritual songs abbout killing children?

Recently a Myspace friend who is trying to convert me sent me a bible with my name (spelled wrong) inscribed on it. It has been over ten years since I've studied the Christian Bible so a read Joshua and Judges. Joshua always made a great impression on me. During this time God spends a lot of time telling the Isrealites to slaughter woman and children. One of their tricks is to send a few men to the gates of a city and attack. When the men inside the city come out the Isrealites run into the woods and the men chase after them. Meanwhile the rest of the Jewish men storm into the city and kill the women and children. Once the men see that their families have been murdered they lose the will to fight and the Isrealites finish them off.

It's all very strange and violent material. I can recall singing songs in church about the "walls come tumbling down." It seems bizarre to have such a spiritual song about killing children.