Do not get involved in a power struggle at this time when a child is seeking to establish his autonomy. Punishment will only make him want to emphasize his independence. Tell your child that persistent thumb sucking can cause a gap between the teeth and inflict sores on the fingers. More extensive approaches include a thumb guard or application of a bitter liquid to the thumb or finger. In most cases, a child will stop sucking her thumb on her own.
Some children take longer than others.
But the experts agree that if you provide a secure and loving environment and positive words of encouragement, you can help your child overcome this behavior.