The state health department says three children were sickened with E. coli after visiting a petting zoo and pumpkin patch last week.
The patients range in age from 15 months to seven years and are from the Twin Cities metro area. They all had contact with animals at Dehn's Pumpkins in Dayton, Minnesota.
One of the children is hospitalized with a serious complication that's characterized by kidney failure.
State health officials say they're following up with others who visited the farm.
"We're concerned that perhaps there are other people out there that visited the pumpkin patch and visited the animals and are now sick and don't realize the potential seriousness of the infection," said Carrie Klumb, a health department epidemiologist.
The department says the farm owners are cooperating with the investigation and they've closed off public access to the cattle and goat areas.