It is very common to see children suck their thumbs. Many parents encourage because it makes children comfortable. However, responsible parents know they must take steps to stop thumb sucking habits of their kids. This habit can cause long term problems for the child. These problems include:

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1. Oral problems: Prolonged sucking on a thumb can change the shape of the mouth and teeth. Children who suck their thumbs tend to have protruding teeth. They are sure to need orthodontics on their teeth when they grow.

2. Irritation of thumb: The skin of the thumb can get excited very badly when the child sucks constantly. It can be very painful for the child. In many cases, the nail grows as twisted due to infection.

3.  Ingesting parasites: Children who continually have their thumbs in their mouths are more at risk of having worms and other parasites in their bodies. This is certainly an unhygienic habit.

4. Teasing by other children: Children who suck their fingers between the ages of 5 and 6 tend to be teased and bullied by other children for being "babies." 

Fortunately, there are some options you can use to get your child to stop sucking his thumb. However, you need to employ a lot of patience to deal with this issue. Parents who use a fun approach to get their child to leave this habit voluntarily are usually much more successful than parents who use force to achieve the same thing.