Authorities believe a child playing with a cigarette lighter started a mobile home fire in south Alabama that killed the young boy and a sibling, the sheriff’s office investigating the fire said Monday.

Investigators found the butane lighter next to a mattress that caught fire in the children’s bedroom, the Mobile County Sheriff’s Office said in a news release. It said preliminary autopsy results indicate smoke inhalation and burns killed 4-year-old Liam Barnes and 2-year-old Noah Gordon when their home burned last Thursday in Irvington, southwest of Mobile.

Sheriff’s investigators said the children’s mother was next door visiting a neighbor when she saw smoke pouring from her home. Kali Sherman rushed inside the burning mobile home and rescued her 10-month-old son from his crib, but couldn’t save the other two.

Smoke detectors inside the mobile home near the children’s bedroom weren’t working, according to the sheriff’s office. It said investigators consulted with local prosecutors and decided no charges will be filed.