To think that, because of their apparent innocence, children cannot become murderers is a tremendous mistake. Sometimes, as is the case with those of the Lord of War or the Islamic State, they are forced to kill in order to survive. Other times they suffer from some mental pathology that leads them to murder, either because of their life circumstances or they simply take pleasure in it. Psychopathic personality structures, from childhood, show a marked antisocial behavior with an uninhibited character. Unfortunately, their disturbance has no age and even as children or adolescents they are impulsive, violent and incapable of forming lasting emotional relationships. They are capable of violence that apparently only adults are capable of. However, the study of these children is often controversial because, as minors, the law does not hold them responsible for their actions. The family origins that have influenced the development of child murderers and their criminal behavior are difficult to determine exactly, due to the complex nature of the cases. But there are also frequent patterns among child murderers: a history of physical, emotional or neglectful abuse and an inability to control their emotions. The authors, César Alcalá, a leading historian, and Blanca Navarro, Doctor of Psychiatry, present a series of cases in order to study the circumstances and resolve each of the cases presented in this essay with an exhaustive forensic psychiatric analysis. Undoubtedly, this is the definitive informative work for all those interested in criminalistics and in understanding the moral behavior of human beings.