My 15-month-old is suddenly waking multiple times at night and crying—why?

The most common cause of a sudden increase in nighttime wakings in 15-month-olds is a sleep regression, which is common at this age. During this period, brain development accelerates; new skills like walking, talking, and social awareness occupy your baby's mind, leading to waking between sleep cycles and reaching for you. Other possible causes: separation anxiety (noticing your absence and becoming worried), upper molars coming in (back teeth usually emerge between 13-16 months and can cause nighttime pain), or a new routine change (caregiver change, house move, starting daycare). This period typically passes within 2-6 weeks on its own. Managing wakings with a calm, brief "check and settle" (preferably without picking up, putting your hand on their back and using a calm voice to soothe) can help. If wakings continue beyond 3 weeks, significantly affect daytime behavior, or are accompanied by fever or ear pulling, consult your pediatrician.