B.R.
I'm certainly no expert in this, so take my opinions as just that. Having worked with children for over twenty years, though, I have seen a number of different problems... mostly the ADD/ADHD diagnoses. In those I've seen many on meds that I felt would have been better off with some other inteventions to help them cope. Probably less than five percent of the ADD/ADHD children I've worked with were ones that I thought were really being helped by medication.
However, though I don't think I've ever worked with a child whose diagnosis was bi-polar, I tend to think in that case getting on the meds as early as possible will be helpful. I base my thoughts on my observation of a few adults I've known who are bi-polar. Again, this is just my opinion for whatever it's worth.