Villains who are willing to hurt and even kill children, unborn or not, which is considered the lowest act of villainy - some of them have succeeded in hurting/killing children, too.

This category also applies to villains who, while they don't directly target children, are still willing to take down or destroy whole worlds, planets, societies, or groups of certain people in a way that would inevitably result in the harming or deaths of children (e.g. Niles and Bill Cipher).

Villains who simply hit children or who didn't effectively kill a child but are willing to let them die in order to achieve their goals (e.g. The Egg) also count.

Kids can also qualify but only if the innocent victim is a toddler or baby and they are at the late ages of a kid usually around 9-12 (e.g. Chara), or if they were formerly kids as villains but eventually grew older later in their franchise they hail from.

Those who purposely try/succeed to kill a pregnant woman or just her unborn child can count as well, since the baby is still technically alive and thus would die right then unless they were to perform a fetal abduction, in which they took the unborn child for themselves.

This category also applies to villains who hurt/kill characters from ages 13-17 (e.g. Sir Benedict Cumbersnatch and Dream), considering 18 is when one legally becomes an adult.

Their heroic opposites are heroes who are nice to children.