ADHD (attention deficit hyperactivity disorder) can't be accurately diagnosed until school age. Before then, the behaviors that characterize it are common among kids: being impulsive, unable to focus, easily distracted, and constantly in motion. So when a 2- or 3-year-old acts this way, it's not time to worry about ADHD. Each week in my medical practice I see active, bright, and curious children -- especially boys -- who have been misunderstood, mismanaged, and wrongly tagged "ADHD" by teachers and parents simply because they can't yet sit still at circle time.
Regard the stage your child's going through now as perfectly normal. But if the behaviors continue -- or get worse -- when he starts school, bring it up with your pediatrician. There are specific diagnostic tests that can help you determine whether your child does, in fact, have ADHD. Meanwhile, discover your busy little boy's "special something," an activity he enjoys doing (probably together with you or another caregiver), and help him practice focusing on that fun task -- whether it involves a sport, music, or art. This may help make him less antsy.