“OK, kids. You have school tomorrow. Time for bed!"

“But Mom! It's not even dark yet!"

Some form of this conversation plays out all over the United States as kids head back to school in the late summer and early fall. And who can blame the kids, right?

You're supposed to sleep at night and be awake during the day. Everyone knows that!

While that's generally true, there are exceptions. Take the siesta, for example.

Many cultures around the world enjoy taking a nap in the early afternoon. Just ask any adult. We're sure they'd love to have a nap during the day!

So why do parents send their children to bed when it isn't completely dark outside yet? Are they being mean? Not at all! They're just looking out for their children's best interests.

Parents know that children need a lot of sleep to be the best they can be during the school day. How much sleep do children need?

For infants, a good sleep should be a whopping 14 to 15 hours. Toddlers need 12 to 14 hours, while school-age children need 10 to 11 hours per night, on average.

If you have to go to bed before dark, it's probably because your parents have calculated what time you have to get up in the morning to get to school on time, and they then set a bedtime 10 or more hours before that.

In many parts of the United States, your bedtime may be at a time when the Sun hasn't fully set yet. This is especially true in the late summer and early fall.

The amount of daylight your area of the world gets each day depends on its latitude. Latitude is a measure of how far north or south you live from the equator.

Because of the tilt of the Earth, the Northern Hemisphere, including the United States, receives the most daylight each year on or around June 21, a day known as the "summer solstice."

After the summer solstice, there is a little less daylight every day until the winter solstice. The winter solstice usually occurs on or around December 20 or 21, and it has the least amount of daylight of any day the entire year.

So, in the late summer and early fall, your parents may set a bedtime that means you're heading to bed while the Sun is still shining. As days go by, though, the amount of daylight will decrease each day, and soon enough you'll be hitting the hay when it's fully dark outside.

You may not like going to bed while the sun is still out, but it could be worse. Around the time of the summer solstice, the North Pole receives 24 hours of daylight. Imagine how hard it must be for Santa and his elves to sleep when it doesn't get dark at all!