A scandal over tainted infant formula spread Monday as authorities acknowledged as many as 10,000 babies may have ingested milk powder laced with the same chemical found in contaminated pet-food exports last year that caused scores of U.S. animals to die. Melamine, a chemical in making plastics and fertilizers, has been used by Chinese businesses to boost protein readings in animal feed and other food products. Pet foods containing melamine-laced ingredients traced to China sickened and killed thousands of dogs and cats in the U.S. last year. Many infants who were fed Sanlu milk powder were stricken with kidney stones....