Do personality and mood disorders manifest early on, at 9 years old, for example? Do depression and bipolar? Do symptoms overlap?
Although 50 years ago it was believed that mood disorders have their onset in adolescence or early adulthood, we now understand that for many individuals, their onset is in childhood. So both depression and mania can occur in a 9 year old. Some symptoms in depression and mania do overlap, especially irritability. There is actually something called a "mixed episode" in which someone has the symptoms of depression and mania at the same time.
Personality disorder is usually not diagnosed until early adulthood because it represents a relatively stable way of interacting with the world. In children, because of the fluidity of development, what might appear to be a personality problem may just be a phase that the person grows out of.