While it is easy to see how the three constructs of introversion, shyness, and Social Anxiety Disorder can get easily confused, and one term may be used to describe another, they are very different from one another. It is vital to distinguish between the three categories because each paradigm requires a different response.
Shyness has, at its core, a fear of negative judgment by others. It's a kind of self-consciousness, not wanting people to look at you and feeling easily embarrassed or easily shamed. It’s the social discomfort one feels when worrying about measuring up or appearing out of place or awkward. If, however, the attention was placed on others, there might be some room to breathe. Finding group activities of interest with children who share those interests may be a way to start, or having the child spend time with people they are already familiar with. Developing assertiveness is another way to teach them to stand up for themselves. Once they are able to set limits, they may feel more in control and less judged.
Introverts on the other hand, may be socially adept but quickly tire of parties or group gatherings where they must be “on” for long stretches. Their social energy is limited, and they guard their supply. They enjoy time alone. Indeed, that is how they recharge. Recognizing their personality type will help you accept some of their behaviors instead of trying to change who they are and thereby affecting self-esteem.
Social Anxiety Disorder is characterized by overwhelming anxiety and excessive self-consciousness in everyday social situations. The anxiety is more intense and persistent than shyness. It escalates to a more chronic fear of being watched and judged by others, and one tends to be very cautious about their behavior in public. Since they feel social humiliation is inevitable they begin avoiding social situations. It might be best to seek professional help if you feel your child might fall in to this category.