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I will not continue a book after the author loses my trust.
Depending upon the tone of the book, killing a child may be the item that kills that trust.
There was a western comedy-satire, written by a black writer, with a racist white narrator and a black bounty hunter main character. It was quite funny, and the white narrator seemed like he was likely to learn something by the events in the book, chasing after his stolen wife with help he has swindled from a black bounty hunter. So I read it and enjoyed the first half.
Then the white narrator let a black child die. The book lost my trust, but I kept reading. Bad mistake.
The main challenge of the book --recovering that kidnapped wife-- was never satisfied, and the black bounty hunter suddenly transformed in the end from a realistic character to some superhuman avatar, and it all collapsed into metaphor and hyperbole.
The ending was so unsatisfying -- enough that I'd almost apply the word "racist" to it -- that I decided never again to continue reading when an author lost my trust. Killing that child meant that the author was promising something other than I wanted, and there was no reason for me to continue reading.
And, if I remembered the author's name, I'd never read another book of his that had a white character.
On the other hand, I've just completed reading "The Pesthouse" by Jim Crace, a lyrically pestilent book where he starts by telling us everyone in Ferrytown is going to die, then introduces us to a 9-10 year-old boy who lives in Ferrytown, and shows us exactly what happens. In Jim Crace's post-apocalyptic America, nature is merciless, and so are the people. Even the baby who the main character cradles through the book is at risk of its life. (...But no spoilers here...)
The difference is, that was part of the promise.
There is only one unbreakable rule: DELIVER WHAT YOU PROMISE.
In my estimate, the promise is the first 1/6 of the work, perhaps the first 50 pages of a typical novel, the first 20 minutes of a typical movie. That's how long you get to set your own rules.
After that, YOU MUST FOLLOW THEM. If you change the rules, you've violated my trust, and there's a trash can with your book's name on it.