A task force of state and national officials was set up on Friday to investigate the cause of the illnesses, as the number of sick children increased dramatically during the day.
The affected children are suffering from diarrhoea and vomiting, and some of them have had in-patient hospital treatment, the newspaper Die Welt reported. The affected states include Berlin, Brandenburg, Saxony and Thuringia, a spokeswoman for the Robert-Koch Institute public health agency told the paper.
Berlin saw the most rapid increase in the number of cases, with some 2,200 children sick by Friday afternoon. Saxony registered 2,000 cases, and Brandenburg 1,500.
Consumer Affairs Minister Ilse Aigner said the goal was "to find the cause of the illnesses as soon as possible and to stop its entry into the food chain."
The food services company, Sodexo, which provides food to the affected schools and pre-schools has questioned its responsibility for the sick children.
“Less than five percent of all the schools we deliver to have sick children,” Sodexo spokesman Stephan Dürholt said on Friday.
“We presume that the cause of the illness is a norovirus outbreak, which we have nothing to do with,” Dürholt said. “The reason that almost all of the children ate food from our kitchens is simply because we deliver food to a lot of schools. We hope that the children feel better soon.”
The Robert-Koch-Institute spokeswoman told Die Welt that it stood to reason that the children were suffering from a food-borne illness, and that some of them had tested positive for the norovirus.
The norovirus, which causes vomiting and diarrhoea, is highly contagious, and can be transmitted by contaminated food or water, infected people, or contaminated surfaces.
The first lab results from the produce used by the food services company were expected Friday afternoon. Many schools in the region were closed as a precautionary measure.