Pesticides, herbicides, antibiotics, hormones are dumped by the ton into our food supply via animal feeds, crop sprays, shipping preservatives, food preservatives, and so on. These poisons end up in our food and also in our water and air. Add to this the massive consumption of sugar which results in swings in blood sugar levels. It has been known for years that low blood sugar can cause depression, fatigue, irritability, even full-blown psychotic episodes. Refined sugar is poison and should not be in the child's diet.
Sugar depresses immune system function terrifically.
It also puts the body on an all-out alert for very survival. Although we simply feels the ups and downs, it eventually destroys it. The body needs to be able to digest whatever food it gets. Even if you eat lots of nice, organic, raw foods, the body may not be able to digest them, so they do little good. This is why some people who try nutritional approaches to managing this situation often meet with mixed results.