Police say the family ordinarily walks with the baby to the El. The 15-year-old mother takes the El to school and the grandmother then takes the baby with her.
However, on Monday, the 15-year-old was off from school so the two were going to visit an aunt together. But, there was some miscommunication about who was going to take the baby.
In addition, police say, the two were trying to figure out how to get on the train by using just one day pass, which is good for just one person.
In surveillance video, the 15-year-old can be seen going through the turnstile at the 60th Street Station, then handing the day pass back to the grandmother, who allegedly intended to use it at the 56th Street Station to avoid suspicion.
After exchanging the pass, the mother and grandmother can be seen on video turning simultaneously after the baby was placed at the gate and walking away, leaving the baby girl behind.
It wasn't until the two met up on the train that they realized the baby was gone.
A SEPTA cashier discovered the little girl and immediately took her into care.
Officers arrived and the baby was evaluated to make sure she was safe and well. DHS was called, but after authorities contacted the mother and grandmother, who were reportedly frantic about the situation, the act was determined to be unintentional.
The women also left their purses and food with the child, which police say made it even more obvious that it was all a big accident.
Officials added that because of their reaction to having left the baby behind, the decision was made not to charge the mother or grandmother with the alleged fare evasion.
The baby is being attended to by the mother, grandmother and great-grandmother.