Three of the children did not have to go to hospital, the release said. But the youngest, a 2-year-old boy, died in a hospital Monday as a result of the illness.
All four children visited animal areas or the petting zoo, which has been closed to the public since the reports.
The symptoms of E. coli can be stomach cramps, diarrhea and vomiting. Some infections are mild, others can be life-threatening. People of all ages can be infected, but young children and the elderly are more likely to develop serious symptoms.
The city asked anyone who had symptoms on or after June 8 to report it to a health care provider.
The disease-causing E. coli types may be transmitted by contaminated water or food or by contact with humans or animals.