Thumb sucking, despite all your hearing, is a completely healthy, natural, and normal activity for your newborn and toddler, in which children usually end this habit by the age of 3 if they start doing so, which has no psychological physical or side effects.
However, some kids do not stop themselves from this habit and if it continues until the age of 4, 5, and 6, your child may already be at risk for some thumb sucking problems. Some problems may be a misalignment of teeth, a lisp, and improper development of the mouth and jaw. You can also buy thumb sucking glove via https://www.amazon.com.au/Age-2-7-STOP-Thumb-Sucking/dp/B00VQU2DZS to stop thumb sucking of your child.
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So how can you stop your child?
1) Taste – There are products that you can put on your baby's thumb that is bad in taste. It is, of course, completely safe and approved by the doctor. It is strengthened with immediate stimulation of thumb sucking is bad with a bad taste of thumb.
2) Praise – When the child does not suck his thumb for a specific time, be sure to praise the child. This provides some positive reinforcement for doing well.
3) Pay more attention to the child – Thumb sucking often continues due to feeling of insecurity and need for rest.
There are more ways but all of the above are very well tested and proven to help any child break the thumb sucking habit. The most important thing to remember is that you should be supported and encouraged to help your child to break the habit.