Why Does My Child Suck Their Thumb Or Finger?

You're Not Alone. Thumb sucking is one of the most common habits during childhood. Most children suck their thumb for safety even before birth. Roughly one out of every three children, ages 1 to 4, will suck his or her thumb at least sometimes. About one in five children will still be doing so at the age of 5 or older. The habit is typically harmless if the child does it occasionally, but thumb sucking is one of the most difficult habits to break.