The criminal investigation didn't begin until Gavin died in April 2015. Because of that investigation, Hailey and Noah were removed from her care.
But when they were returned in August 2015, she killed Noah less than a week later.
Her guilty plea to two counts of murder and one count of involuntary manslaughter took the death penalty off the table, the Columbia Dispatch reported.
Her defense team had argued that she had suffered repeated sexual abuse and beatings as a child, and had also suffered lead poisoning, which may have left her brain damaged.
"Brittany's brain is broken," attorney Kort W. Gatterdam said before sentencing on Tuesday. "And no one ever helped her."
Ohio Attorney General Dave Yost said in a statement: "A guilty plea cannot undo the heartless acts this woman committed against defenseless children — she does not deserve to be called mom. But locking her up will at least guarantee she won't be able to repeat this evil."
Pilkington will not be eligible for parole for 37 years.