Thumb sucking
Lots of babies suck their thumb or fingers. It is part of the normal reflex infants have to root for food. As a survival technique, the sucking urge is strongest in the first three months of life. After the age of six months or so, it has more of a calming influence and helps relieve stress. If your little one sucks his thumb or fingers, especially when he’s tired, don’t get upset – it’s normal.