The boy was unchained to eat and use the bathroom, said Mike Daniels, a police spokesman.
Police said Pollard is the mother of six children - four boys, including M.P., and two girls ranging in age from 7 months to 11 years. Craig is the 7-month-old girl's father.
Shortly after 3:30 p.m. Monday, Pollard called police to report that M.P. had run away, police said. A resident then called police to report that he had found a child a few blocks away.
M.P. told police he was chained in his mother's bedroom as punishment and forced to sleep on the floor uncovered at night, police said. He also said his hands were occasionally restrained with zip ties.
"This level of depravity inflicted upon a child is chilling," Camden County Police Chief Scott Thomson said a news release.
A woman who said her former husband owned the four-bedroom house said Pollard and her children secured the rental property through the city's housing authority and moved into it in May.
"She was so excited with the house because she said the kids would have space to play," said the woman, who drove by the blue two-story house Tuesday and declined to give her name.
Child Protection and Permanency, the state's child welfare agency within the Department of Children and Families, was given custody of M.P. and his five siblings.
"He could have been seriously injured or died had this continued, so to get this child and his brothers and sisters out of that environment was critical," Sgt. Janell Simpson, supervisor of the county force's Special Victims Unit, said in a statement.
Pollard and Craig were being held Tuesday in the Camden County Jail on $50,000 bail each.
Contact Darran Simon at 856-779-3829 or at email@example.com, or follow on Twitter @darransimon.