Nighttime settling difficulties (i.e., bedtime resistance, sleep-onset delay) occur in about 25% of young children and are associated with attentional, behavioral, and emotional problems. We examined whether the timing of internal (endogenous) circadian melatonin phase (i.e., dim light melatonin onset; DLMO) and its relationship with parent-selected bedtimes were related to nighttime settling behaviors. Fourteen regularly napping preschoolers (8 females; 30-36?months) participated in a 6-day protocol (parent-report of nighttime settling, actigraphic assessment of sleep onset latency, evening salivary DLMO). Average DLMO clock time was 07:40?p.m. ± 00:48?minutes, occurring 29?minutes ±?32?minutes prior to bedtime (lights-out). Children with later DLMOs had longer sleep-onset latencies (r = 0.62) and poorer success in falling asleep r = -0.59). Children whose bedtimes were closer to their DLMO had longer sleep-onset latencies (r = 0.72) and increased bedtime resistance (r = -0.54). We conclude that dissonance between parent-selected bedtimes and children's circadian physiology may contribute to the development of nighttime settling difficulties in early childhood.