The district attorney announced those charges Monday against Adrian Morgan Allen, 27, of Gooseneck Road in Bristol Township.
D.A. David Heckler said he will seek the death penalty in this case.
At his arraignment Monday, a judge ordered Allen to be held without bail. Allen had nothing to say to reporters as he led from his arraignment.
Police say Allen was babysitting his girlfriend's three children at an apartment in the 2500 block of Knights Road in Bensalem on the weekend of February 24th to 26th.
Heckler said Allen swung the girl around causing massive head trauma. Heckler went on to say that the girl lay for a better part of a day, grinding her teeth, before her mother arrived home and took the child to the hospital.
The girl died early Wednesday morning, police said, a little more than a week after the assault.
An evaluation showed injuries consistent with child abuse including serious internal bleeding in her skull that required emergency surgery, evidence of blunt force trauma to her head, an adult-sized bite mark on her arm, broken ribs, an arm fracture and bruising all over her body.
? According to the affidavit, Allen told police he forced the child to walk over and throw out her own dirty diaper, despite her having a broken leg.
He allegedly said she had tried to support herself with a stack of wooden chairs when the chairs came crashing down on her. Later, court papers say Adrian told police he kicked her in the head while wearing boots.
But authorities aren't sure if these were cover stories.
"It is possible that the child's head struck the chairs, but not because she caused them to fall on her," Heckler said.
Allen's attorney, Charles Jonas, says it's too early to comment.
"We were just assigned pretty recently. We have some investigating to do, so we don't really know a whole lot," said Jonas.
Allen was previously charged with first-degree felony aggravated assault and child endangerment charges.
There was no word from police on if the children's mother faces charges as well. The victim's 5 and 8 year old sisters are staying with their grandmother, and the D.A. said he did not know of any signs of abuse on those girls.