"Sucking is very natural for babies,
"It's very common for them to use their thumbs or fingers as part of their routine to find comfort and to soothe themselves."
At this stage, not only is thumb or finger sucking common, it is considered harmless in terms of a child's growth and speech development. The questions most parents ask themselves, however, is how long should it go on? Should a child still suck her thumb when she is ready for preschool?
Dental problems and prevention
"Usually, a child who is in the 2- to 4-year range will start to develop other coping skills beyond thumb or finger sucking, such as language development,"
We used to think that as long as a child stopped sucking by the time they developed their permanent teeth there would be minimal impact on the mouth and jaw,"
Thumb sucking generally stops by the age of 5 years. Some older children will retain the habit, which can cause severe dental problems.