Most children begin sucking their thumb or finger from a very young age; many even start inside the womb. Sucking is a natural reflex for an infant and it serves an important purpose. Sucking often provides a sense of security and contentment for a young one. It can also be relaxing which is why many children suck their thumbs as they fall asleep.
According to the American Dental Association, most children stop thumb-sucking on their own between the ages of two and four. They simply grow out of a habit that is no longer useful to them. Studies show that the older a child gets, the lower his chances of continuing to suck his thumb. However, some children continue sucking beyond the preschool years. If your child is still sucking when his permanent teeth start to erupt, it may be time to take action to help them to break the habit.