There are several sources from which a child can carry this trait. One of the most important and obvious ones is the ambience. If the child is living among people where there are more arguments than discussions the child is likely to get scared.
It has also been noticed that if one of the parents is susceptible to fear, the child is likely to develop it. Watching their parents get anxious prompts kids to pick up this habit easily.
Kids who have overprotective parents tend to fear almost everything; and this is because of the passive anxiety that their parents have. A child who has been brought up to be dependent will always feel helpless and will be scared to face the world.
Kids who go through separation like parental separation or are separated from their parents from an early childhood are likely to be more fearful than others.