Feelings of shyness or discomfort in certain situations aren't necessarily signs of social anxiety disorder, particularly in children. Comfort levels in social situations vary, depending on personality traits and life experiences. Some people are naturally reserved and others are more outgoing.
In contrast to everyday nervousness, social anxiety disorder includes fear, anxiety and avoidance that interfere with daily routine, work, school or other activities. Social anxiety disorder typically begins in the early to mid-teens, though it can sometimes start in younger children or in adults.