For a long time, people thought that babies who sucked their thumbs, fingers or pacifiers did so because they were improperly nursed or that the bottles they were fed had inferior nipples. But these musings don't explain why ultrasound pictures show fetuses in utero with their thumbs in their mouths. Besides the oral impact, you have to consider the importance of the thumb to the child. It's a security for most kids. They enjoy it.
Kids suck because they're bored, frightened, anxious, hurting, sick or sad.
Maybe it also becomes a habit. By the time a child is three, it's worth discussing the issue with your dentist. But even at that age you can't intervene very much because the child is not old enough to benefit from intervention techniques, McConnachie notes. Don't try to force the issue too soon or you'll cause him distress and yourself grief. According to research published in the Journal Of Clinical Pediatrics, thumbsucking diminishes substantially with age.