Health officials say a 3-year-old boy from the Denver area died from an E. coli infection on Friday.
It's not clear where he lived but the investigation is being handled by the Tri-County Health Department, which covers Adams, Arapahoe and Douglas counties.
Officials are trying to track down the source of the infection.
Authorities say the boy attended a day-care center in a private home. Twelve other children attend the center, and they are being tested.