Hi TexasRob,
You may want to read this topic which is pinned at the top of the forum:
Bipolar ChildrenI'm going to keep this brief as I'm certainly not an expert with this subject but there are those here who are very knowledgeable and will be able to give you some personal examples.
Bipolar is the name given to Manic Depression these days so they are the same disorder. There are different types of bipolar too and it is pretty difficult to get a diagnosis, especially in children. However there are many children who do exhibit the symptoms. There is in fact the case study of a nine year old in the topic above. Like you said they often are diagnosed with other disorders.
I have a nephew with attachment disorder who behaves pretty like this but he is only 4 and he hasn't learned how to deal with his emotions yet.
Visit the Bipolar forum and our meds forums to find out about the different medications. There are many combinations available although I'm not sure if the options are more limited for children. Lamictal I think is quite common though, although I may be wrong about that.
It's definitely not strictly a medicine problem and there will be things that you can do however I'm not the person to tell you what these are. I would think there may be some books available on the subject because you're not alone in this.
Like I said, this isn't something I know a lot about but I am sure others will come along with a lot more insight to help you out. There are a great many resources on this site though so have a look around and let me know if I can help you in any way.
PRT xx