Thumb sucking is perfectly normal for infants; most stop by age 2.  Thumb and pacifier sucking habits will generally only cause a problem if they go on for a very long period of time. Most children stop these habits on their own.  If your child does not, discourage it after 4 years of age. Prolonged thumb sucking can create crowded, crooked teeth, or bite problems. Dr. Chan will be glad to suggest ways to address a prolonged thumb sucking habit.