A baby girl has died, and four other children under the age of 8 are in hospital after they were accidentally exposed to a poison reportedly used for pest control in a Fort McMurray apartment.

Five children were rushed to hospital after a reported chemical spill in a main floor suite of an apartment at 81 Fraser Avenue in Fort McMurray Sunday afternoon.

The eight-month-old baby girl died in hospital. On Monday, four of her siblings were still being treated: three boys aged 2, 4, and 6-years-old, and a 7-year-old girl.

The youngest and the oldest boys were airlifted to the Stollery Children’s Hospital, while the other two remained in hospital at the Northern Lights Regional Health Centre in Fort McMurray.

“The children are still in critical condition, and they are being treated as such,” Cpl. George Cameron with Wood Buffalo RCMP said.

RCMP also confirmed the mother was in hospital as well.

“The mother as well, she is at the hospital here in Fort McMurray under observation,” Cpl. Cameron said. “The father, it is our understanding, did not receive any injuries as a result and he is with his children in Edmonton.”

RCMP told CTV News on Monday that the substance used was believed to be some type of fumigant used in pest control.

A relative of the family told CTV News the children’s mother had used a chemical she brought back from Pakistan to try and kill bed bugs last Tuesday.

However, on Saturday, all five children started showing symptoms of poisoning, specifically vomiting.

Officials with the Municipality of Wood Buffalo said Regional Emergency Services and RCMP are monitoring conditions inside the suite – and said the air quality was affected by phosphine, a poisonous substance used as an insecticide.

All other units in the building are safe, officials said.

RCMP called the death of the child sudden, and not criminal – but the incident is under investigation.

“We look for any type of evidence that will help us determine what happened and that happens through statement taking, the whole 9 yards,” Cpl. Cameron said.

“We just want to try and see if we can get something in place that will ensure something this tragic will not happen again.”

With files from Dan Grummett