The Chicago Public Schools District plans to start teaching children sex education in kindergarten. Its Board of Education passed the new policy Wednesday.
The policy mandates teachers spend a set amount of time on sex education lessons at every grade level.
Across the country, most public schools begin teaching sex-ed in fifth grade.
Under Chicago's new policy, kindergartners will learn about basic anatomy, reproduction, healthy relationships and personal safety.
"It is important that we provide students of all ages with accurate and appropriate information so they can make healthy choices in regards to their social interactions, behaviors and relationships," Barbara Byrd-Bennett, the CEO of the Chicago Public School System, said in a statement.
"By implementing a new sexual health education policy, we will be helping them to build a foundation of knowledge that can guide them not just in the preadolescent and adolescent years, but throughout their lives," she said.
The Windy City has the third largest public school system in the country.
Parents will be allowed to opt their child out of the sex education program.