Sleep regression in babies often happens between 4 and 18 months of age, and is marked by a decrease in the quality and duration of their sleep. Some common signs are shortened naps, skipping naps, increased crying while sleeping, difficulty settling down for sleep, night awakenings (waking up more times than usual), turning over and sleeping on the tummy during the night, waking earlier than usual in the morning, waking and fighting bedtime, as well as resisting bedtime routines.