BEIJING, China (CNN) -- A third baby has died and at least 6,200 children have fallen ill after drinking formula tainted with the same chemical involved in a massive pet food recall last year, Chinese officials said Wednesday.



China's largest producer of milk, Mengniu Dairy Group, announced the recall of three batches of formula made in January after tests showed they were contaminated with melamine, said Li Changjiang, China's director of quarantine and inspection.



Though it should not be added to food ingredients, suppliers in China sometimes put it in food to make a product appear to be protein rich. Melamine has nitrogen, and standard tests for protein in bulk food ingredients measure levels of nitrogen.



More than 1,300 infants are hospitalized with illnesses including malnutrition, kidney stones and acute renal failure.



On Monday two brothers were arrested who Chinese officials say supplied three tons of milk each day to the Sanlu Group, which makes baby formula.  Watch crowds of moms get their babies tested »



They could face death if convicted, according to state-run newspaper China Daily. The siblings' raw milk had been watered down and a chemical added to fool quality checks, the newspaper said. Watch who has been arrested »



Sanlu Group, one of China's leading dairy producers, has recalled more than 8,200 tons of the tainted formula following reports of sickened babies, news agency Xinhua reported. The manufactured also sealed off more than 2,100 tons of contaminated product, and another 700 tons still need to be recalled, according to Xinhua. Watch angry parents demand answers at Sanlu »



Investigators said the brothers confessed to watering down the raw milk and mixing in tripolycyanamide, also known as melamine. The paper reported the siblings did it to recover losses suffered when the factory rejected earlier milk shipments, and that 19 other people have been detained for questioning.



Recalls of the products by the Yashili and Suokang companies have been made, and of China's 175 baby milk powder production companies, 66 have already stopped production, Li said. Investigators are testing samples at the remaining factories.  Learn more about the chemical melamine »



China's Xinhua news agency reported that worried parents started lining up at 5 a.m. Wednesday to see doctors at Renmin Hospital in Shijiazhuang, the capital of the northern Hebei Province.



Wang Lifang said she went to the hospital after medics at her local hospital 28 miles (45 kilometers) away in Xingtang County found problems with her two-month-old daughter.



"The county hospital found my daughter has kidney stones that are smaller than 4mm [less than a fifth of an inch]," the farmer in her 30s told Xinhua.



"My daughter is so young that the doctors worry the stones might not be washed out themselves so they told me to go to the provincial hospital."



The report said the girl had drunk a little water.



"Doctors said I better not feed her powdered milk," Xinhua quoted a "tearful" Wang as saying.



"In the past few days, I fed her fresh milk bought from a neighbor who raises a cow but once I left home I did not know what to do."



Other parents told Xinhua they wanted their children scanned for kidney stones as a precaution.



Peng Jing, a mother in her 20s, said her 2-month-old son had drunk about two small bags of Sanlu powdered milk.



"He seems OK, but we want to be 100 percent sure he is healthy so we came to have the tests," she told Xinhua at Renmin Hospital.



The food safety scandal prompted China agricultural officials to start a nationwide inspection of its dairy industry.



Health experts say ingesting melamine can lead to kidney stones, urinary tract ulcers, and eye and skin irritation.



The chemical is commonly used in coatings and laminates, wood adhesives, fabric coatings, ceiling tiles and flame retardants.



Chinese investigators have found melamine in nearly 70 milk products from more than 20 companies, Li said Wednesday. Products made by Sanlu had the highest concentration of the chemical.



It is not the first time Sanlu has been connected
What is the number of sick babies? What type of chemical was found in the formula? What is China's largest milk? What are concerned parents doing? What is the name of the group? How many babies are ill? How many babies are now known to be ill? What is the name of the chemical tainting the milk? Who recalls batches of formula
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question: What is the number of sick babies?, answer: at least 6,200 | question: What type of chemical was found in the formula?, answer: melamine, | question: What is China's largest milk?, answer: Mengniu Dairy Group, | question: What are concerned parents doing?, answer: started lining up at 5 a.m. Wednesday to see doctors | question: What is the name of the group?, answer: Mengniu Dairy | question: How many babies are ill?, answer: at least 6,200 | question: How many babies are now known to be ill?, answer: 6,200 | question: What is the name of the chemical tainting the milk?, answer: melamine, | question: Who recalls batches of formula, answer: Mengniu Dairy Group,