"The age range in which children drop to just one nap per day is usually between 12 and 18 months, but the most common age to drop to one nap is between 14 and 16 months," Jill Spivack, LCSW, licenced psychotherapist, pediatric sleep consultant, cofounder of Sleepy Planet Parenting, and coauthor of The Sleepeasy Solution, told POPSUGAR.