The latest child to die in a series of abuse cases that has rattled the city's child welfare agency was slammed into walls and beaten by his mother's boyfriend while she did nothing to stop him, police said.

Investigators believe 4-year-old Quachaun Brown died Sunday following a beating by Jose Calderon, who later claimed he was angry because he thought the child caused a television to fall over, police said Tuesday. The child's mother, Aleshia Smith, didn't report any trouble until early Monday.

Smith, 26, was arrested Tuesday on a manslaughter charge; Calderon, 18, was charged with second-degree murder.

It was unclear whether the suspects had attorneys, and prosecutors had no comment.

Police said they suspect the abuse began last summer, after Calderon moved into the apartment with Smith, Quachaun and his four sisters. Two of the girls, ages 6 and 9, have told investigators that the boyfriend singled out the boy for regular beatings, which included shoving him face-first into walls.

Autopsy results were pending, but police said there was preliminary evidence that the child had a fractured skull, a damaged liver and atrophied leg muscles.

Police responding to a 911 call around 3 a.m. Monday found Quachaun dead in the family's filthy Bronx apartment. They said the apartment was in disarray, with cold air blowing in through a broken window, no food in the refrigerator and the children poorly clothed.

Smith had told police the television fell on the boy Sunday and that he began vomiting blood the next day.

In November, Administration for Children's Services caseworkers had visited the apartment and reported it "to be in order," agency head John Mattingly said.

The agency underwent a shake-up after the Jan. 11 death of 7-year-old Nixzmary Brown, who was allegedly tortured, abused and beaten by her stepfather. Reports of her suffering had been made to several agencies, including schools, police and child welfare. Her death followed recent homicides of three other children known to the agency.