A New Jersey woman and her 1-year-old son died, and her 3-year-old daughter was in very critical condition, after their car filled up with carbon monoxide from a snow-filled exhaust pipe, police said on Sunday.

The 23-year-old mother and her children were warming up inside the car as their father was shoveling around it just after 8 p.m. on Saturday night. They were parked only a few blocks away from their Passaic home.

But as the father shoveled, the exhaust pipe was stuffed with snow, and carbon monoxide slowly filled up the inside of the car, police in Passaic said.

When the father went to check on them, he immediately noticed they were unresponsive, police said.

Emergency personnel performed CPR on all three victims, and they were taken to St. Mary’s Hospital in Passaic. But the mother and her young son didn’t make it.

The 3-year-old girl was in very critical condition on Sunday and transferred to St. Joseph’s Regional Medical Center in Paterson.

Police said this tragedy is a reminder to make sure your exhaust pipe is clear of snow or debris when clearing it off or warming it up.