How about, when there are no family values instilled as a child, when the school system passes you through with esteem certificates and free meals, you don't learn to value anything, including a life.
To these kids, killing a baby was no different than stepping on a bug.
Feral scum don’t need a motive.
They were never taught to fear the disapproval of father or mother.
They were never in any danger from the authorities, so no fear there.
And they have not been taught that they are accountable for their actions and one day will stand before a righteous God.