Seven people have been infected with E. coli O157 at Sutton Park in Sutton Coldfield over July and August.
Five of the cases involved children under eight years old, according to the Health Protection Agency. All patients have since recovered.
BBC News reports posters and leaflets have been issued, but the HPA said parents may want to use other parks for the time being.
Dr Roger Gajraj, a consultant with the HPA’s West Midlands East Health, said extra hand washing facilities had been set up in the park.
Posters issued by Birmingham City Council in Sutton Park recommended keeping children and pets away from grazing animals and washing hands, particularly before eating or drinking.
They also advised washing shoes and bicycle and pushchair wheels after a visit to the park.