
I was just looking more into this, because the sentiment that daughters are more difficult than sons always irked me. In my mind, boys would objectively be harder to raise every time because they have a propensity to behave worse, struggle with school, get in fights, break laws, etc. compared to girls. Part of it is the brain’s slower development in boys, but another part is that many parents falsely assume boys are able to left alone and neglected at an earlier age in childhood
No one’s done an experiment where they raised a bunch of boys and girls in the same way to factor out cultural differences, so we will probably never know for sure. But it is related to puberty. Not sure what factors influence timing of puberty, but young girls have been entering puberty younger over time. Presumably this shift is because of better nutrition, but hormones in food and other factors could be at play