There is no doubt that the medications employed to treat symptoms of mood disorder carry possible side effects that are more serious than the side effects of the stimulant medications employed to treat ADHD. The important consideration, though, is to select a medication that properly addresses the target
symptom(s). Accurate diagnosis is a worthwhile goal, but keep in mind that medications are used to treat symptoms, not to treat conditions. With children, particularly very young children, is is difficult to know whether, for example, temper outbursts or volatility is due to a behavior problem, to a condition such as Oppositional Defiant Disorder, or to a Mood Disorder (Depression or Bipolar Disorder). When multiple conditions are suspected, and ADHD is one of the conditions, it is often the case that pharmacological treatment commences with stimulant medication and then subsequently, if necessary, with other medications (such as antidepressants, mood stabilizers, etc.). It sounds like you are doing a prudent thing my proceeding with a careful evaluation, from which can ensue a coherent treatment plan, to include pharmacological treatment if indicated. Remember to keep focused on the target symptoms when it comes to medication (and other treament, e.g., psychotherapy) as well.