The answer is that if you give an infant under a year cow’s milk, the infant can develop microscopic gastrointestinal bleeding (you don’t see it in the diaper), and this can lead to anemia and other problems. Yogurt does not cause this same reaction. Now: WHY does this happen? It seems to be the milk proteins that are responsible for this mild allergic reaction. In yogurt or infant formulas, the milk proteins are “de-natured” by heat in such a way that this allergic reaction does not happen.