I'm weary of childhood bipolar diagnoses and alot of personality disorder diagnoses in young adults. I was misdiagnosed ADHD, the stimulants made me manic while in effect and depressive while the effects were wearing off (can you guess the next diagnosis in the sequence?), Bipolar! And because I didn't want to take the medications I also got slammed with ODD in the process. The Bipolar medications made me just out of it and all over the place. Depressed, catatonic, manic, enraged... et al. So by the time I was a teenager I was labeled with NPD, BPD, and HPD traits, but taken off of the Bipolar medications and they threw in PTSD chronic as a consolation prize.
It took me until I was 25 to sort through the mess of diagnoses. What was really going on was a mixture of long-term abuse by drug addicted parents coupled with having Asperger's Syndrome. The problem is that so many of these disorders overlap in their symptoms.
Bipolar is fluctuating moods of depression and mania, someone with an ASD could easily portray these symptoms because of high anxiety mixed with being ostracized for their awkwardness. They can also be misunderstood just because of their affect and obsessively strong interests and beliefs.
BPD is severe fear of abandonment portrayed in catastrophic ways (suicidal ideations/gestures, threats, outbursts of anger to perceived abandonments). Someone with an ASD because of their life-long battle with acceptance into a social milieu that can be very cruel to those who are different, could fear being abandoned again and catastrophize those emotions with an intensity that could be mistaken for a BPD episode at times. Even due to sensory overload... I've sat in a corner screaming, "I want to die!" more than once just because I was overwhelmed with everything going on in my environment at the time.
Anti-social, Schizoid, and Narcissistic personality disorder could easily be misdiagnosed in someone with ASD because of their lack of need for social interactions.
And of course all of the above could be misdiagnosed for one or the other in an adult. Children by nature are irrational and impulsive so to accurately diagnose them with a severe mental disorder/personality disorder, I think, should be done with the greatest of caution, if at all!