" When kids stay up late, their stress hormones like cortisol kick in, which makes it harder to fall asleep,” wrote Dr. Laura Markham of Aha! Parenting. “The problem is that cortisol stays in the system and makes them edgy the next day; it also contributes to depression, anxiety, and weight gain. The famous moodiness of teenagers is partly attributable to late bedtimes, which have become standard practice in our culture. Just because your toddler gains the ability to keep himself awake doesn’t mean you’d let him stay up half the night. Just because your tween and teen gain the ability to keep themselves up doesn’t mean it isn’t bad for them. "

― Tricia Goyer , Calming Angry Kids: Help and Hope for Parents in the Whirlwind