Parents of preschoolers with attention deficit hyperactivity disorder (ADHD) may be advised to give their child medication to help them concentrate, sit still and/or control impulsive behaviors. A new study comparing two classes of medications might help them arrive at a decision...The new study, which appears in the May 4 issue of Journal of the American Medical Association, is said to be the first to compare the two classes of ADHD drugs in preschoolers. The drugs target different brain chemicals.