Your baby is born with a normal and necessary desire to suck, the intensity of which varies from child to child. At any time after birth, your baby may begin to suck her thumb or finger, even her lip or tongue, to satisfy that urge. Breast feed babies are less likely to become thumsuckers, because mothers generally allow them to linger longer at the breast than bottle fed babies at the bottle.
When baby is weaned, the need to suck for food declines, but sucking usually of a thumb or a pacifier continues to be a comforting and calming activity for the child. It is not a sign of significant tired, upset or bored, or when she is or trying to fall asleep. You need teeth slightly. Neither effect is long lasting. Most likely, she will drop the habit by kindergarten age. Trying to talk her out of it before she is ready may only increase her determination. Arm restraints, bitter coatings and adhesive strips are not effective.
If thumsucking persists beyond the age of six, however, the child risks displacing the upper permanent teeth, and she should be discouraged from continuing thumsucking. The way to do this is indirectly, by dealing with the causes of the behavior rather than by for biding it. For example, if the youngster sucks when she is tired, try an earlier bedtime. Counter boredom with parental attention or stimulating play, hunger with a snack and so on.