Brittany Pilkington, 23, was charged with three counts of murder on Tuesday and is in jail, said police in Ohio.
A mother who calmly called 911 to report that her baby son wasn't breathing later admitted to police that she had killed him and her two other sons over the past year, authorities said.
Brittany Pilkington, 23, said she took their lives because her husband paid more attention to them than their three-year-old daughter, according to authorities in Bellefontaine, Ohio.
Logan County prosecutor William Goslee, who interviewed Pilkington, told The Columbus Dispatch: "In her mind, she was protecting her daughter from being not as loved as the boys were by their father."
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Pilkington was charged with three counts of murder on Tuesday and is in jail.
She is accused of killing three-month-old Noah Pilkington, who passed away on Tuesday, as well as four-year-old Gavin, who passed away in April, and three-month-old Nial, who died in July 2014.
Her daughter, Hailey, has since been taken into custody by a county child welfare agency.
Officers went to the family's apartment on Tuesday morning after Pilkington called 911 to say that Noah wasn't breathing. She was calm as she answered a dispatcher's questions while the baby's sleep apnea alarm beeped in the background, police told the Associated Press.
The baby boy was pronounced dead at a hospital.
His death came as authorities were already investigating what had happened to the other boys, who were found unresponsive by their father when he returned home from work. Their causes of death still hadn't been determined.
Pilkington's uncle told the Columbus Dispatch that Hailey and Noah had been in the custody of children's services following Gavin's death but were returned to their parents this month.
Goslee said the children were handed back to their parents after a coroner determined the deaths weren't suspicious.
Investigators said there is no evidence that Pilkington's husband had anything to do with the deaths, WBNS reported.
Police Chief Brandon K. Standley said in a statement on Tuesday: "The tragic deaths of Niall, Gavin and Noah leave a pit in our stomachs today. Our condolences go out to the remaining family members who have supported this family through a very difficult 13 months."
The Ohio Bureau of Criminal Investigation is assisting local authorities.
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