You should consult a Naturopath to find out what foods are best for your
son. But here is some background info to get you started:
A whole-foods diet is recommended for ADHD children. Food allergies have been debated as a possible cause of hyperactivity and attention deficit disorder and salicylates may negatively affect some children. Salicylates are found in artificial colors and flavors, aspirin, grapes, tomatoes, green and red bell peppers and many other foods.
More info on this subject can be found in this article on ADHD