Please give me a (non fictional) example of a culture in which people are ok with other people murdering their children for religious reasons.
It wasn't always other people do the sacrificing. There is the Biblical story of Abraham and Isaac. Even if you consider the Bible as fictional, the story likely has at least some basis in fact.
Child sacrifice - Wikipedia - mentions, among other theories, it's believed that in Maya culture, parents would allow their children to be sacrificed, thinking they would continue to exist in some form even after the sacrifice.