This article as well as several other news articles that I have seen recently discusses psychiatrists in New Zealand and Australia that are prescribing Ritalin to children under six years of age - though this is against the drug company's warnings, as these drugs have not been tested for children at this age. So, in addition to exposing very young children to the myriad side effects of this powerful ADHD, it's not even tested for them, and it could have other short and long term effects on these kids.
I have spoken to people who have taken Ritalin and Prozac. It made them either incredibly irritable, or numb. They were unable to feel happy or sad, and unable to appropriately react to situations in life. Not letting a young child be a young child, and instead putting them on mind altering drugs is not right.
Check out this site for more information on what these drugs do to a person.