The two women, whose names were withheld by SEPTA, the Southeast Pennsylvania Transit Authority, attempted to use a single one-day pass to pay both their fares, but in the maneuver accidentally left the daughter's infant girl in a stroller near a cashier's booth Monday morning, the Philadelphia Daily News reported.
"The grandma thought the mother was going to bring the baby through the gate for strollers and wheelchairs, and the mom thought grandma was taking the baby with her," SEPTA spokeswoman Heather Redfern explained.
That left the two women on the train illegally, and the baby at Philadelphia's 60th Street Station, the newspaper said.
The cashier in the booth took the baby inside to keep her warm, Redfern said, adding the women notified police and returned to be reunited with the child.
"We normally would have cited the people who were involved in the fare evasion, but given the traumatic experience they had gone through, and because they were visibly upset, we did not cite them," Redfern said.