An Alaska elementary school is under investigation after children were served floor sealant instead of milk at a daycare summer program, Anchorage Daily News reports.

The incident took place on Tuesday at the Sitʼ Eeti Shaanáx̱ Glacier Valley Elementary School in Juneau. Shortly after breakfast was served, students complained of the milk tasting bad and burning their throats. 

“It was found that the milk served was actually a floor sealant resembling liquid milk. Staff immediately directed students to stop consuming the substance and removed it,” the school district said in a statement. 

Juneau School District Superintendent Bridget Weiss confirmed to Anchorage Daily News that a school official contacted poison control following the incident, which resulted in at least one student being treated at a local hospital.

According to Weiss, the mix-up happened because the floor sealant was “stored or moved on the same pallet as large pouches of milk that were also in cardboard boxes.”

“We don’t know how that happened, but they were all put on the same pallet,” she said. “That pallet was delivered, and the assumption was that it was milk because that’s what we thought was being delivered.”

An investigation into how the mix-up occurred is being led by the Juneau Police Department. However, Weiss maintained that the investigation is “not really because we believe there’s anything criminal or mal-intent at this point, but we do want a thorough investigation of what happened, how it happened, and they’re trained investigators.”