Here is a fascinating story from the New York Times about the middle period of childhood, from about five or six until puberty, when kids begin to make sense and learn to be good little people. Apparently, modern humans are the only hominins blessed with this desultory development. Neanderthals, our immediate human predecessors, apparently were all grown up by twelve.
There have been articles about how as the length of human life was extended human culture was developed. The grandmas and grandpas were around to pass along knowledge from generation to generation to generation. They were available to care for children, allowing parents to hunt and gather without toting along a child. Now it appears that the extension of the human lifespan also extended childhood to enable children to become more, well, human. And a lot of that humanizing occurs by the hormonal cues going on in a child's body.
Said to begin around 5 or 6, when toddlerhood has ended and even the most protractedly breast-fed children have been weaned, and to end when the teen years commence, middle childhood certainly lacks the physical flamboyance of the epochs fore and aft: no gotcha cuteness of babydom, no secondary sexual billboards of pubescence.
Yet as new findings from neuroscience, evolutionary biology, paleontology and anthropology make clear, middle childhood is anything but a bland placeholder. To the contrary, it is a time of great cognitive creativity and ambition, when the brain has pretty much reached its adult size and can focus on threading together its private intranet service — on forging, organizing, amplifying and annotating the tens of billions of synaptic connections that allow brain cells and brain domains to communicate.
Subsidizing the deft frenzy of brain maturation is a distinctive endocrinological event called adrenarche (a-DREN-ar-kee), when the adrenal glands that sit like tricornered hats atop the kidneys begin pumping out powerful hormones known to affect the brain, most notably the androgen dihydroepiandrosterone, or DHEA. Researchers have only begun to understand adrenarche in any detail, but they see it as a signature feature of middle childhood every bit as important as the more familiar gonadal reveille that follows a few years later.