Thumb, Finger, & Pacifier Habits
Do not be overly concerned if your child is very young, and still sucking on his or her fingers or thumbs. Children will typically stop this behavior all by themselves. If your child continues to suck on his or her fingers or thumbs after three years old, Dr. King might recommend a mouth appliance that prevents the behavior.
Prolonged behavior of this type can cause teeth to grow out improperly or in a deformed direction toward the lip, causing language and eating problems.