A 3-year-old boy was killed and his 2-year-old sister was critically injured when they were hit by a freight train Tuesday morning in northwest Indiana.

The crash happened about 9:30 a.m. on the CSX railroad tracks south of the Woodland Village Mobile Home Park in the 5700 block of U.S. Highway 20 in Portage, Indiana, according to a statement from Portage Police Chief Troy Williams.

The toddlers may have snuck out of their home in the mobile home park through a screen door and made their way toward the tracks, Williams said. The train’s conductor told investigators he blew the horn and tried to brake when he saw the children on the tracks, but was unable to stop before the train hit them.

The boy was dead when emergency crews arrived, according to Williams.

The Porter County Coroner’s Office identified him as Caleb Wilson. An autopsy was scheduled for Wednesday.

Paramedics tended to the girl until the University of Chicago Aeromedical Network flew her to Comer Children’s Hospital, where she was in critical condition, Williams said.

A CSX spokeswoman said the train involved in the crash was a Norfolk Southern train that had permission to operate on the CSX tracks.

Norfolk Southern did not immediately provide further information Tuesday afternoon.

The crash remained under investigation by Portage detectives.