The alleged beating happened two years ago, but police said a friend convinced the girl to report it just last month.
Cedric Jones, 27, Sharon Jones, 45, Cecila McDonald, 25 and Lonnell McDonald, 27, were arrested Tuesday and charged with engaging in criminal activity.
The fifth suspect, 22-year-old Robert Joseph Cayald, was arrested for the aggravated assault of a child.
Cayald is accused of raping the alleged victim in an apartment in August 2012 while she was staying with family members.
According to police documents, when four of the suspects later found out about what happened, they got nervous because they didn't want Child Protective Service removing their children.
Police said they took matters into their own hands.
Sharon Jones gave the girl emergency contraception pills, court documents say.
When that didn't work, Sharon's daughter, Cecila McDonald, allegedly held the girl's arms while Cecila's husband, Lonnell, sat on her pregnant belly and bounced.
The affidavit goes on to say that Sharon jones called her son, Cedric, Jr., to come over to her house, where he kicked and punched the girl repeatedly.
At one point, Cecila McDonald yelled, "You ain't about to get my kids taken away from me!" according to court documents.
The girl told police she was in extreme pain during the assault that last six hours. She was about eight months pregnant at the time and delivered a stillborn baby a few hours later.
The victim was not given any medical attention at the time.
The suspects are also accused of trying to dispose of the baby's body in a charcoal grill. They ended up throwing the remains out in plastic bag, police said.
When that didn't work, the affidavit says that Sharon Jones offered to pay her son $25 to take care of it, so Cedric Jones, Jr. put the remains in his trunk and stashed them in an unknown location.
The remains have still not been found.
During a press conference Wednesday, police commended the girl for being brave enough to come forward about the "heinous crime."
Seven children living in the home with her were placed in foster care. She is also now in CPS custody, but is living with a friend.
"I mean, it's sad," said neighbor Precious Ridgell. "'Cause like, who would do that to a young girl? It wasn't her fault."
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