Now, I wonder about that.
In many primitive cultures, children grew up watching a number of their younger siblings being murdered at ages 0-3 because there was not enough food to go around. One Polynesian woman recounted tearfully how she had killed 17 of her own children. The children were best seen as killed, not murdered, because it was legal to kill those kids. In many cases, murder itself is more of a legal term than a statement of fact about some type of homicide.
Anyway, keep in mind that a number of adults in these cultures have grown up watching their younger brothers and sisters being killed or murdered (pick your term) by their own mothers. In our society this would cause incredible harm, and many would become adults who were scarred long-term or even for life by seeing such things. Yet studies of adults who witnessed such murders throughout childhood have struggled to find any harm at all from this practice. As adults, most agreed that it was sad or even tragic but that this was a necessary thing to do in their cultures. Either we killed those kids or we all died. That was the choice.
There are Amazonian tribes where 13 and in some cases 12 year old girls can consent to sex psychologically and even legally. I don’t agree with that, but within the framework of that culture, it seems to work. Those men have been having sex with and marrying girls that age for as long as anyone knows. Careful studies have been done on the women of these tribes who married adult men at ages 13-15 and sometimes at age 12. Absolutely zero harm from early marriage to adult men was found in all cases.