"Thumb sucking is a natural reflex for children. Sucking on thumbs, fingers, pacifiers or other objects may make babies feel secure and happy and help them learn about their world. Young children may also suck to soothe themselves and help them fall asleep." - ADA
It may look darling, the sweet, peaceful look of a child sucking their thumb but it can cause severe problems if allowed to continue through the years.
Depending on how the thumb or fingers are placed in the mouth while sucking on them, the damage can be quite severe.
What can you do to help your child stop sucking their thumb?
1) Praise your child when they are not sucking their thumb or fingers
2) Focus on correcting the cause of any anxiety that could be leading to thumb sucking
3) STOP or similar nail polish thumb sucking deterrent
4) Your child's dentist and/or orthodontist have additional measures that can be taken to stop this habit.