Diagnosing bipolar disorder in children is difficult. Specifically because there are no definitive physical signs that indicate bipolar disorder.
There also is no specific test that your doctor can give to a child to determine if he is suffering from the disease. As far as testing is concerned, the best that he can do is to test for other diseases for which there are tests, and rule those diseases out, one by one, until bipolar disorder remains as the most likely cause of the child's mood swings.
In addition, to help with his diagnosis, the doctor will want to have a detailed history of any kinds of mental problems in your family such as depression, suicides, and so on. Unfortunately, getting a diagnosis for your child may be a long and drawn out process. Unfortunately, at the present time, bipolar disorder has no cure, only treatments. So if your child is diagnosed with bipolar disorder, the doctor can then recommend certain types of treatments.
In most cases, when an adult is treated for the disease, prescribed medications are at the top of the list in preferred treatments. With children, however, you have to be extremely careful when recommending powerful drugs. For one thing, your child's body is still developing and you don't want to interfere with that process by exposing him to ill advised drugs.
Secondly, although most of the prescribed drugs have been tested to a certain extent on adults, practically none of them have been tested extensively on children. And, finally, many of these drugs have side effects, such as weight gain or other more serious effects, that are not good for your kid.
So, when giving your kid drugs, the best approach is to work closely with your doctor to limit the amount of medication that you are giving to your child as well as monitoring the effects of the drugs on his body. And, once your child is on medication, never stop giving him the medication without your doctor's approval. Some drugs have powerful withdrawal symptoms which can trigger even worse bipolar disorder reactions in your kid.
In addition to prescribed medications, in many cases, therapy may be advised as well. Therapy won't cure the disease, but it can make it more manageable for the child. Therapy may involve the rest of the family as well. It can greatly help them in learning how to deal, as a group, with the disease and generally make life better for everyone in the family.