Occasional bad dreams are normal at all ages after about 6 months of age. When infants have a nightmare, they cry and scream until someone comes to them. When preschoolers have a nightmare, they usually cry and run into their parents' bedroom. Older children begin to understand what a nightmare is and put themselves back to sleep without waking their parents.
Some dreams are good, some are bad.
Dreams help the mind process complicated events or information. Frequent nightmares may be caused by violent TV shows or movies. Explain to your child that she was having a bad dream. Sit on the bed until your child is calm. Provide a night-light, especially if your child has fears of the dark.