A US mother in Ohio admitted killing her three young sons in separate incidents over the past 13 months because her husband paid more attention to the boys than a daughter, police said.

Brittany Pilkington called 911 shortly after 3:00 am Tuesday to report that her three-month-old baby, Noah, wasn't breathing.

Police said they immediately began a "tedious investigation" because it was "the third such incidence at this same residence involving similar circumstances."

Another three-month-old son, Niall, was found dead byfather JosephPilkington when he came home from work in July last year. The cause of death was not determined.

Then on April 6, the father came home to find their four-year-old son, Gavin, was also dead.

Brittany Pilkington was charged with murder after sheconfessed "she intentionally killed all three of her sons," police said in a statement.

She reportedly killed them by putting a blanket over their heads and suffocating them because her husband paid more attention to the boys than he did their daughter, who will turn four later this month.

"In her mind, she was protecting her daughter from being not as loved as the boys werebytheir father," Logan County Prosecutor William Goslee told the Columbus Dispatch.

Noah and his sister Hailey had been removed from the home because the police were investigatingGavin's death. But a judge sent them back earlier this week after a coroner determined that neither Gavin nor Niall had died of suspicious causes, the paper said.

Brittany Pilkington's uncle was appalled that the children were returned to the family.

"Why would you give them back after a little boy just died and when you’re in the middle of an investigation?" Joe Skaggs told the Dispatch.

Gosleesaid child protective services typically try to keep families together, but added, "I've been aware, and concerned about, this family since this first child died."

The Bellefontaine, Ohio police department said the deaths "leave a pit in our stomachs."

"Our condolences go out to the remaining family members and friends who have supported this family through this very difficult thirteen months."