It is my opinion that supplements work better when they are combined, this is how they are in your food and the body can digest and separate them for proper metabolism. Besides, optimum nutrition involves all of the ingredients working together.
This does not just apply to young children, but all people. Taking a food grade multi vitamin, adding fish oils (DHA and EPA) and eliminating poor food choices will improve brain function with more stable emotions.
If the cigarette manufacturers put chemicals in the cigarette to make it more addictive, maybe, just maybe, the processed foods that are so addictive may have some of the same additives in them. This is just speculation; there is no proof, yet.