Back in the day, kids with ADHD were labeled as the hyper kids - the ones with tons of energy on the playground. Nowadays of course, they have a 'disorder'. This study found that almost 1 million children are potentially misdiagnosed because they are the youngest and most immature in the kindergarten class. This suggests a serious flaw in classification criteria like the DSM-IV which could have adverse consequences for victims of misdiagnosis.
Kids at a young age are interpreting the world, trying to make sense of it and developing their schemas so it is natural for them to want to take in as much of their environmental stimuli as possible - thus concentrating less time on one specific task or stimulus. ADHD drugs are stimulants which if taken in spite of a misdiagnosis will have developmental effects on the neurology of the child's brain - and not necessarily a positive one, more likely is a negative rewiring of the child's brain.
http://www.sciencedaily.com/releases/2010/08/100817103342.htm