The cortisol awakening response (CAR) in 2- to 4-year-old children: effects of acute nighttime sleep restriction, wake time, and daytime napping.
Gribbin CE, Watamura SE, Cairns A, Harsh JR, Lebourgeois MK. The cortisol awakening response (CAR) in 2- to 4-year-old children: effects of acute nighttime sleep restriction, wake time, and daytime napping. Dev Psychobiol. 2012 May; 54(4):412-22.