The children who were found dead in a Lynnwood town house that caught fire Sunday were a 7-year-old boy and 15-year-old girl, according to South County Fire of Snohomish County.

The children, who were siblings from Shoreline, were visiting a relative who lived in the town house with his partner and her 11-year-old son, South County Fire spokeswoman Leslie Hynes said. The county medical examiner’s office had not yet identified the children as of Monday afternoon.

Firefighters responded to reports around 2:30 p.m. of flames coming from the town house, which is on the second floor of a seven-unit building in the 6700 block of 196th Street Southwest. The firefighters found the couple and 11-year-old boy outside. When they entered the home in an attempt to rescue the other children, they found that they died.

The 11-year-old boy was treated for smoke inhalation and was released Sunday night, Hynes said. The two adults were not injured. One firefighter suffered a minor injury but has since been released from the hospital.

Fire investigators are still determining the cause and origin of the fire. The town home is heavily damaged, which has complicated the investigation. Investigators are looking at whether the town home had fire alarms, Hynes said. They will wrap up their investigation at the scene Monday night but don’t expect to have a determination right away.

South County Fire, Lynnwood Police Department and the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) were at the scene Monday, Hynes said. The Snohomish County Fire Marshal’s Office is also involved in the investigation.