CHICAGO (WGN) — Five children were taken to hospitals Wednesday after reportedly smoking a vape pen in gym class at a Chicago elementary school.

The children were taken to local hospitals after reportedly “smoking a substance” at Harvard Elementary School in Chicago’s Grand Crossing neighborhood just before 2 p.m. Wednesday, according to the Chicago Fire Department.

A source told WGN that the students were on a field trip to Lincoln Park Zoo on Tuesday when one of them picked up a discarded vape pen and brought it to school on Wednesday.

Fire officials said several students then used the vape pen during gym class. It’s unclear what substance it contained.

The children involved are reportedly 9 to 10 years old and are all in good condition, fire officials said.

WGN reached out to Chicago Public Schools for comment but has not gotten a response.