The bedtime you select for your toddler may be out of sync with his or her internal body clock, which can contribute to difficulties for youngsters attempting to settle in for the night, according to a new University of Colorado Boulder study.

The study pinpointed the time when the hormone melatonin increased in the evening, indicating the start of the biological night, in a group of 14 toddlers whose sleep also was studied over the course of six days.

The study showed that toddlers with later melatonin rise times took longer to fall asleep after being put to bed, CU-Boulder Assistant Professor Monique LeBourgeois said.

"This study is the first to show that a poor fit between bedtimes selected by the parents of toddlers and the rise in their evening melatonin production increases their likelihood of nighttime settling difficulties," LeBourgeois said.

Toddlers with longer intervals between the onset of nightly melatonin release and their subsequent bedtimes were shown to fall asleep more quickly and had decreased bedtime resistance as reported by their parents, according to the study.

BDST: 1555 HRS, JAN-28, 2014