PHILADELPHIA (AP) — Police say three seventh-graders were taken to a hospital from a west Philadelphia elementary school after ingesting treats that may have been laced with an unknown substance.

Police say they were called to Martha Washington Elementary School shortly before 11 a.m. Monday, where a 13-year-old girl reported feeling lethargic after consuming the Rice Krispies treats.

She was taken to Children’s Hospital of Philadelphia and listed in stable condition. Another 13-year-old girl and a 12-year-old girl were also taken to the hospital and were also listed in stable condition.

Police are investigating; it wasn’t immediately known what the substance in the treats, if any, may have been. The school said school district police were notified immediately and “a full investigation of this incident is ongoing.”