Many a times, all these are from birth and sometimes these mood swings certainly malfunctioning of brains and many a times difficult to cope with for the person who are affected with. 

Yes. This disorder Bipolar disorder should be identified at the earliest. If it is unnoticed, it becomes a bigger problem in the future.

Yes I agree that this can be noticed in children and an observant parent can take corrective steps so that the child's behavior become more balanced 

Most of the parents will not have the patience to know the reason for Mood swings. They mistake it as Naughtiness and they beat the children which in the long run prove counter productive. The child becomes defiant over a period.

According to Henner, renowned food scientist and neurologist, even small amount of processed foods can cause mood swing for sometime and produce negative mood with observable dipping of energy levels. 

Mood swings should not be overlooked. As this Bi polar disorder if untreated in time will lead to further complication like "Defying and Juvenile delinquency."

This topic brings to my mind something that happened in my school a couple of years ago.One of the high school students was good at his studies and generally quiet and well behaved and after the Dasara holidays there was a change in his whole personality and behavior that was noticeable .He began falling back in his studies became more and more boisterous and when checked at class for his bad behavior he became abusive, even pushed one of the lady teachers.When the parents were told about this , they simply washed their hands off saying that he was a teenager now and hormones were doing that to him.We also came to know that he came from a joint family and the family was going in for a division of property and there was a lot of infighting, even violence between the members and the matter was in the police station and the civil court.

After a couple of more incidents the fellow was asked to leave school if he did not behave himself.But there was no use since he only became worse and he was sent home with his TC.The parents made a big noise and he was again brought back with strict warning to parents that he should go for counselling...Thankfully they did and he did improve but never like he was before.I wish the parents had kept a close watch and taken preventive steps earlier.

While bipolar disorder cannot be prevented, it's important to be aware of early warning signs of an impending episode of bipolar disorder.. Fear of being neglected is one of the causes for Bi Polar disorder. Constant observation of the child by the parents and an adequate Medical help can protect the child from this malady

I remember a Tamil film “Anniyan” (outsider), with Vikram in the main role, and directed by Shankar. A Brahmin youth was dissatisfied by the corruption in society but he was helpless because he couldn’t do anything against it. With his suppressed feelings he developed a “multiple personality disorder”, by which assumed different identities. Sometimes he became a strange person with unbelievable physical power and eradicated the corrupted persons from society by killing them brutally. Next moment he becomes the poor Brahmin youth. I think this “multiple personality disorder is the extreme state of this bipolar disorder.

Exactly.  Behaviour changes frequently for an a rason that can't be understood by outsiders is an extreme case of Bipolar disorder.