The Necessity of Sleep, by Alice Marsh, Detroit, Mich., 1903, Primary Education Magazine, Health Talks with Youngest Children I.
"...I wonder if we realize how much lack of sleep is responsible for the irritability and nervous restlessness that we see, not only in children, but in adults as well. It is simply the nerves crying out for rest and nourishment, and they cannot get the one without the other. For some unexplained reason, the human is the only animal that rebels at bedtime. We have all seen children so sleepy that they are pained in trying to keep awake, begging to sit up a little while longer.
...How long should little boys and girls sleep? If they are eight years old, or younger, they need at least twelve hours. That means, if you get up at seven o'clock in the morning, you should be asleep at seven o'clock the night before. And why should you stay up longer? To play? You can do that before the sun goes to bed—between the time when school closes and supper. That is the very best time of the day for playing."
I guess my children are old fashioned. They always need(ed) an early bed-time - asleep by 7 p.m. and up twelve hours later.