When does a child start to dream? and at what age do nightmares or night terrors begin?

Before birth: Rem (rapid eye movement) sleep, the stage of sleep when most dreaming takes place, is present before birth, and at birth comprises about half the sleep cycle, declining gradually to about 25% into teenage and adulthood. Nightmares occur during rem sleep, but night terrors occur during deep non-rem sleep. Both can start during infancy.