The child needed dialysis overnight, according to Health Minister Xavier Bertrand, who visited the hospital in the northern city of Lille at midday Friday. Medical staff say that his condition is fluctuating.
The six other children affected, who are aged between 20 months and eight years, are in a stable condition.
Bertrand repeated assertions that the E coli strain is not the same as the one that has killed 38 people in Germany and one in the Netherlands, although the minced beef which appears to be the origin of the infections came from slaughter houses in both those countries.
The boss of SEB, the company which sold the meat to the Lidl supermarket chain, complained that results of analysis of samples of the beef are taking an “abnormally long” time.
Guy Lamorlette said that he feared for the future of his company, which employs 180 people, because of media coverage of the outbreak.
The company has recalled all the meat in question and Lidl has withdrawn all SEB’s “Steak Country” minced beef range from sale but 10,000 packages are reported to have been sold already.
Consumers are advised to check if the use-by date is 10-12 May 2012.
Experts say that the contamination could have taken place at a slaughterhouse. The bacteria is commonly found in cattle's intestines and could have been passed to the meat if the two came into contact.