Hey, more than three-quarters of infants suck their thumbs or fingers through the first year of life.  Many children stop sucking their thumbs on their own sometime during the toddler years — between ages 2 and 4.  Thumb sucking isn't usually a concern until a child's permanent teeth come in. At this point, thumb sucking might begin to affect the roof of the mouth (palate) or how the teeth line up. So its common wait for another year