Two pupils from Redfield Edge Primary School were hospitalized while a third is recovering at home.
The school has closed its reception and year one classes until further notice as a precaution.
Parents of a "number of other children" have reported their children have upset stomachs and diarrhoea, with some experiencing more "severe symptoms."
Dr David Hunt, from the Health Protection Unit, said: "At this point, E. coli O157 is suspected, not confirmed, but we wish to be precautionary.