Both children and adolescents can develop bipolar disorder. It is more likely to affect the children of parents who have the illness. Unlike many adults with bipolar disorder, whose episodes tend to be more clearly defined, children and young adolescents with the illness often experience very fast mood swings between depression and mania many times within a day. Children with mania are more likely to be irritable and prone to destructive tantrums than to be overly happy and elated. Mixed symptoms also are common in youths with bipolar disorder.

If bipolar syndrome occurs at an early age, there is a larger risk for a more severe illness than if it occurs later in life. Because of this, it is important to give treatment as early as possible.

Older adolescents who develop the illness may have more classic, adult-type episodes and symptoms.