CASTRO VALLEY, Calif. — Four-year-old Ahmeir Diaz-Thornton couldn’t sit still in class and rarely ate his lunch. While his preschool classmates spoke in perfect sentences, Ahmeir had trouble pronouncing words. Ahmeir’s preschool teacher relayed her concerns to his mother, Kanika Thornton, who was already worried about Ahmeir’s refusal to eat anything but yogurt, Chef Boyardee spaghetti, oatmeal, and applesauce. He also sometimes hit himself and others to cope with the frustration of not being able to communicate, she said. Thornton took her son, who is on Medi-Cal, California’s Medicaid progra…