How Do They Know?

How do kids know when there is an important day the next day? Is there some static in the air that something that requires me to wake up early is going to occur? Therefore sending them into a late night adrenaline rush? I don't get it?! It never fails, when I have to get up in the morning and my sleep is vital to my success for the following day they stay up and cry and whine and demand things;

"Drink!"
"Songs"
"Book"
"Pee"
"Lay with Me."
"I don't like these PJ's."
"I'm hungry."
"I can't sleep."
"I hurt myself."
"Cut my nails."

On and on, over and over, they say the same things and fight sleep tooth and nail. Why can't they just lay in their beds and slowly drift off into dreamland? WHY???