Stories including those which later became sacralised in the Bible were all written by humans, there cannot possibly be evidence that it was otherwise.
The plot line of a story reflects and reveals a society and its values. From reading ancient literature and plays today, we are conscious even now of reacting to the high drama of moral dilemmas, they give the tale its interest and the reason for our emotional engagement. No doubt the silly story of a man who promises his god a sacrifice of the first person who comes to greet him, was a literary chestnut from early times. Only a reckless idiot/murderer would think literally of doing this but set in the context of child sacrifice familiar to the readers (or more likely presented to the audience as a play) it would make for a gripping presentation.
The Hebrews were part of the Canaanite culture, their language originated with the Phoenicians and its alphabet is shared with early Hebrew and Samaritan. The Israelites also inherited religious cues and values from them.The Phoenicians were famous for their tophets or places for child sacrifice and the inhabitants of the Levant as with many of the those dwelling on the Mediterranean coast, followed the same practice.
Biblical accounts do naturally reflect the great shifts in religious horizons and as the Hebrews learned from their Egyptian overlords they adopted a form of montheism (actually henotheism) centering on YHVH who was one of the the sons of the Phoenician's God El. Much of the ranting and threats by Jehovah in the OT is about this new concept namely exclusively worshipping only one of the many gods. It was to put an end to polytheism. The story of the human sacrifice of Abraham's son Isaac originally had Isaac killed but the "new light" was that no longer is human sacrifice a good idea, so in the retelling of the ancient story, the one included in the sacred texts, Isaac is spared and the message is that animal sacrifices will do the job.