CHICAGO (CBS) — A health scare at a Chicago elementary school sent four children to the hospital on Thursday.

Officials were called Thursday around 1 p.m. to Locke Elementary School, in the 2800 block of North Oak Park Avenue, for reports of several elementary school students falling ill.

The school said administrators called after learning several students “may have ingested an unknown substance.”

In all, first responders checked out 10 children at the scene. Four students were transported to the hospital as a precaution, but are expected to be okay.

It is still unclear what the students ingested and how they got sick.

Chicago Public Schools said a review of the situation is currently underway.

This is a developing story. Check back for more details.