There has been a publication about artificial colors and other food additives influencing children's behaviour (McCann, 2007), making it more ADHD-like. This is perhaps due to the chemicals' influence on brain chemistry. This claim is not new, just the methodology (double-blind, randomized). I just checked out this paper and figured out the corresponding E numbers. Unfortunately the research used "cocktails" of these additives and therefore some of these might be harmless. But nevertheless, here is the list: