Thumb sucking (or pacifier sucking) is a part of nearly every child’s early years. When they’re little, this sucking motion is often a comforting, subconscious habit.
As a parent, there’s no reason to be concerned about the use of these “security blankets” when your child is very young, but if your child is still sucking his or her thumb and/or fingers after permanent teeth erupt (usually around the age of 5 or 6), they may be putting themselves at risk for problems later in life. (FYI, the pacifier should be LONG gone by this point!)