It is not a behavioral issue. Some children, like your son, are
shyMultiple system atrophy by temperament. He is very young, and it's reasonable at this age to encourage him and continue to expose him to social situations, but do not presssure him to interact beyond what he is capable of right now. As he develops further you will see what unfolds, and don't be surprised as he gets into preschool and other
schoolPreschooler development
Preschooler test
Preschooler test or procedure preparation
School age child development
School age test or procedure preparation
School-age children development situations if he warms up to the social situation. While he may always be somewhat
shyMultiple system atrophy, he may well interact in a way that can be regarded as normal. He needs your support and encouragement, so try to maintain your equanimity and please do not regard his behavior as a behavioral problem.
I belong to a support group for teachers and parents of children suffering from anxiety and if this is the issue, I assure you that the anxiety will not go away nor will your son outgrow it. I do know that children three and four years of age can learn to manage their fears in months; older children at six and seven years usually take years to manage their fears. Teenagers seem to be especially resistant to treatment. It might be wise to speak to your son's pediatrician and, if necessary, ask for a referral to a person with experience in treating anxiety disorders. I wish you the best ...