This is the best time to make him interact with many people and kids. Never allow him to get isolated. Good that you caught this problem earlier and his career can now be shaped very well. Pls ask him to read the book in loud voice and make him energetic/happy . Encourage boldness in him and he need your closer support and care. Never shout at him and don't push him hard, be very soft to him. Your aim should be to make him a early class stage speaker and a bold/brave orator so that stuttering demon will get killed on the way.