It's name means "child death" because that's what it does. Invisible to adults, Der Kindestod preys on weak children by sucking the life out of them. After it is threw with the child, the death looks as if by natural causes. It sucks the life out of a child through tentacles that extend from its eyes.

When a horrible flu raged through Sunnydale, Der Kindestod made it's home at the Sunnydale Hospital. Unfortunately for it, Buffy was admitted after falling prey to the virus. In her weakened and hallucinegetic state she was able to see Der Kindestod. After talking to the children she realized that there was more going on in the hospital then just the flu. But she had only had a glimpse of the creature and she didn't yet know what it was. At first she believed that the doctor in charge of the children was the one who was killing them. But when he was murdered by an invisible being right in front of her, she knew she was dealing with something supernatural.

She put Giles and Cordelia on research mode while she and Willow tried to figure out a way to stop the being. Buffy remembered how she had witnessed Der Kindestod while having a raging temperature, so she deliberately gave herself the flu virus in hopes of being able to fight the demon. The flu made her almost too weak though and she almost failed. But at the last moment she was able to break its neck and kill it before it killed her.