One quote in this article, about how children were "easier to control" before television "exposed" them to the "world of adults," is pure bullshit. Ask any parent or teacher, from any era, and they will tell you that any child is a challenge. In my experience working with children, I know that they can be demanding, unruly and even vicious (particularly toddlers and toddlers with hormones, aka adolescents). Anyone who's read The Lord of the Flies is familiar with the fear that, if left to their own devices, meaning outside the influence of television, children will devolve into pre-civilization savages.
This is probably one of the reasons the "evil child" is such a compelling narrative device. Children, with still developing senses of empathy and morality, feel they can act without consequence and, as a result, are very self-centered. The evil child is a regular child's selfishness and occasional cruelty taken to its logical extreme.
The portrayal of the young Lord Voldemort in "Harry Potter and the Half-Blood Prince" is mentioned, and, connoisseur of evil and deviance that I am, while watching, I noticed the signs of a psychopath in training in the portrayal of young Tom Riddle. As a child, he is cold, unfeeling, with an inflated sense of his own self-worth and a tendency to bully other children and torture animals. Animal torture is, of course, one sign of a future serial killer. As an adolescent, he uses careful flattery and superficial charm to get what he wants, the psychopath's mask of sanity.
My obsession with crime began with Columbine, a mass murder perpetrated by two teenagers. In a new book on the subject, the author interviews a forensic psychiatrist who concludes that Eric Harris, one of the killers, was a fledgling psychopath, a cold, manipulative egomaniac who considered everyone else inferior and, therefore, deserving of their fate. His partner, Dylan Klebold, was suicidally depressed and angry at the world, but with the inertia that comes with depression, was unable to act on his feelings by himself. When the psychopath with something to prove collided with the depressed boy with a death wish, they exploded.
The scariest "evil kid" I've read about is Jesse Pomeroy, the "Boy Fiend" of Boston in the late 19th century who, at 14, was sentenced to life in prison for two torture murders. At an age where most serial killers are still dismembering dead dogs or tormenting family pets, Pomeroy, the product of a poverty-stricken family and a viciously abusive father, had already graduated to human victims. He tortured several children before killing a four-year-old boy and a ten-year-old girl. Most teenage killers fall under the categories of school shooters, going into their school with guns to let out aggression, or thrill killers, bored kids who kill for profit or out of twisted curiosity. But Pomeroy was disturbingly focused on his own sadism as his motive, his murders matching the savagery of adult murderers like Jeffrey Dahmer or Andrei Chikatilo. Even before television, the moral watchdogs of the time found a sinister pop culture object to blame for Pomeroy's crimes, in this case the lurid dime novels popular among the nation's youth. When he was captured, Pomeroy was originally sentenced to death, but, because of his age, this caused a public outcry, and his sentence was changed to life in prison.