Adrian Morgan Allen, 27, of both Gooseneck Road in Bristol Township and Camden, N.J. faces first-degree felony aggravated assault and child endangerment charges.
Police say Allen was babysitting his girlfriend's three children at her apartment in the 2500 block of Knights Road in Bensalem between Friday night and Sunday.
It was on Sunday when Allen allegedly called his girlfriend to say that her daughter was sick and vomiting.
The girlfriend returned home, police say, to find the child unresponsive in her crib. The mom took the baby to St. Mary Medical Center and the child was then flown to St. Christopher's Hospital for Children where she was last reported to be in critical condition.
The exact circumstances of the assault were not disclosed by police.
Anyone with information is asked to call the Bensalem Police Special Victims Unit at 215-633-3658.
Allen is currently in Bucks County Prison on 10% of $1 million bail.