Nightmares are scary dreams that wake children up and make them afraid to go back to sleep. Nightmares may happen for no known reason, but sometimes occur when your child has seen or heard things that are upsetting. These can be things that actually happen or are make-believe.
Having bad dreams every once in a while is normal at all ages after about 6 months of age. Nightmares often relate to developmental stages of a child: toddlers may dream about separation from their parents; preschoolers may dream about monsters or the dark; school-aged children may dream about death or real dangers. Nightmares most often happen during the last third of sleep, during REM (dream time) sleep.