Until the middle of the twentieth century, it was generally believed that children were not affected by mental disorders. Today, however, most medical professionals agree that nearly every mental disorder present in adults can affect children as well. The Institute of Medicine estimates that 12 percent of children in the United States—about 7.5 million boys and girls under the age of eighteen—have some type of brain disorder.

Before it was accepted that children could suffer from mental illnesses, many people believed that a child’s emotional and behavioral problems were the result of outside factors, such as bad parenting. Parents were advised that such problems would disappear if they exerted more discipline, or if mothers stayed at home with their young children, or if fathers were more attentive. Some people even believed that the children’s...