CHARLOTTE, Mich. (AP) — Authorities in Michigan say a 6-year-old boy’s condition is improving a day after his three siblings were killed when their horse-drawn buggy was struck by a motor vehicle.

Police believe the four were returning home from an Amish school Wednesday when the crash occurred near Charlotte in Eaton County. The children who were killed were aged 8, 10 and 13 years old.

Undersheriff Jeff Cook says it’s an “unspeakable loss” for the parents. Jerri Nesbitt of the sheriff’s office tells WILX-TV that the 6-year-old boy had a “good night,” despite leg and head injuries, and was in stable condition.

The buggy was struck from behind. The elderly driver of the motor vehicle was examined at a hospital. The crash remains under investigation. No names have been released.