How can I help to improve the mental health of a child who is having mental abnormality?

When you first come on a site like this, you should spend a few minutes to read the FAQs and learn how this site works. You posted this in a Discussion thread that had absolutely nothing to do with your question. So I moved it to a more appropriate place. Did it ever occur to you that there was a reason for all those forums you scrolled past?

As to your question, we really can't answer that without knowing what the abnormality is. If the child truly has a mental health issue, the child should be under the care of a qualified physician. The physician can then advise you of how to deal with the issues.