INVERNESS, Ill. (WGN) — A suburban Illinois father allegedly poisoned his children before he died by suicide, killing his son and putting his daughter in critical condition, police said.

Woo Chang, 41, and his 10-year-old son, Austin, were found dead Sunday after officers were called at about 4:20 p.m. to a home in Inverness to conduct a well-being check.

The boy’s 6-year-old sister was found inside and taken to a hospital in critical condition. Police said the cause of death was carbon monoxide poisoning caused by fumes from a generator.

Police met with the children’s mother, who told said the children did not return at the scheduled time with her estranged husband. She was the one who found her children inside the home.

Autopsies are scheduled for Monday.