The mother of a 3-year-old Chester County boy beaten to death in 2014 pleaded guilty Wednesday to  third-degree murder.

Jillian Tait, 33, and her boyfriend, Gary Lee Fellenbaum III, 25, were accused of ongoing abuse, which included striking Scott McMillan and his 6-year-old brother with their fists as well as frying pans, metal rods, and whips.

Police said the adults taped Scott to a chair and beat him unconscious, and hung both children upside down by their feet to pummel them. Scott died following a series of beatings between Nov. 2 and 4, 2014, in Fellenbaum's home in West Caln Township, police said.

Tait also pleaded guilty to conspiracy to commit first-degree murder, endangering the welfare of children, assault, and related charges on Wednesday at the Chester County Justice Center in West Chester.

Prosecutors said they would pursue the death penalty for Fellenbaum. Tait's plea prevents her from receiving the death sentence prosecutors had sought for her as well. She faces a maximum sentence of 64 to 128 years in prison.

Michael Noone, the county's first assistant district attorney, told County Judge William P. Mahon that prosecutors reached the agreement with Tait because she has accepted responsibility, is less culpable than her former boyfriend in her son's death, and is cooperating. She agreed to testify against Fellenbaum. Prosecutors said Tait's actions may have contributed to Scott's death, but Fellenbaum's actions caused it.

Fellenbaum's trial is scheduled to start in September. Lawyers agreed not to discuss the case outside of court.

Amber Fellenbaum, Gary Fellenbaum's wife, was in the home at the time of the abuse but did not report it. She pleaded guilty Wednesday to all four charges against her: two counts each of endangering the welfare of children and reckless endangerment. She faces a maximum sentence of nine to 18 years in prison.

She also said she would be willing to testify against Gary Fellenbaum.

The judge will sentence both women after his trial.