Although it is quite fair to want your kid to stop thumb sucking it may be helpful to know that some of the dangers of thumb sucking may not be based on facts. You can get more information on how to stop thumb sucking via https://stopthumbsucking.org/thumb-sucking-appliances/.
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The myths
1. My child is still sucking his thumb at 12!
Not likely. Statistics show that less than 9% of children who suck their thumbs still at the age of 5 years, with the vast majority break the habit between the ages of 2 and 4. Most will stop as they begin to identify with their peer groups and do not want to be the one to kindergarten with their thumb in mouth in storytime.
2. It will ruin her teeth
This may be true, but only after the children get their permanent teeth, which begin to occur between 6 and 8. In older children, sucking a chronic thumb can start changing the shape of the oral cavity. Fortunately, the vast majority of children have stopped than their own anyway.
3. He uses it as a crutch
It is true that young kids who discover their thumbs are used for comfort, it does not necessarily mean they will not be able to learn coping mechanisms to deal with stress later in life.
4. A pacifier is better
Many parents tell me they prefer a pacifier because at least they can take away the pacifier. But in my experience, many parents say that and then do not really take off! If the pacifier is their sleep child accessory, and they use it for comfort, it becomes equally difficult to remove the child.
So with these common fears on the way, there's really no right or wrong, only personal preference of the parent.