Auditory hallucinations as a child, bipolar disorder?

Well it's possible but it's more likely to have been schizophrenia. To be diangosed with bipolar at such a young age it must have pretty bad. Maybe they misdiagnosed schizophrenia if they were not aware of the voices? If you see the doc or psych for a review tell them about the voixces and see what they say. Not really necessary to have anti-psychotics at this stage if you don't have any current symptoms. Keep an eye on things.