Authorities said the children came dangerously close to being swept away after entering the river, where water levels and currents had risen following heavy upstream rain earlier in the week.
"It's scary, you never know what could happen," said Kyle Cash of Bryn Mawr, who was fishing on the river with his son.
Bridgeport Police Chief Todd Bereda said one of the children was in a particularly dangerous situation.
"At the time, the water level was about chest high for the one child, and the other child was struggling to hold on to the older child at that point," Bereda said.
The incident unfolded near Frosty Falls in Bridgeport Borough.
Police said an officer spotted the children in distress while driving across the DeKalb Street Bridge. Before firefighters arrived, the officer and a nearby SEPTA repair crew took immediate action to help the children.
"They got up on the trestle, and they guided the children to a better place of safety to await final rescue from the fire services," Bereda said.
Swift-water rescue crews from Bridgeport and Norristown responded along with firefighters from Upper Merion. The rescue operation lasted about 45 minutes, according to Chief Bereda.
It is not uncommon to see people in the water in that area, but investigators believe the children may have ventured out too.
Franck Kiser, who operates Pegasus Rowing nearby, said the river can be deceptive.
"Even though it may seem a lot shallower after the dam there, the current ... one slip and you could be out of control heading downstream," Kiser said.
The children, described by police as elementary and middle-school-aged siblings, suffered minor injuries.
"They were fearful; you could see it in their eyes, and they were just glad to be out of the water," Bereda said.
The children who live nearby were reunited with family a short time later, according to authorities. Their mother declined to comment on the incident.
Police urged anyone entering the water to understand local conditions, know their abilities and use appropriate safety equipment when necessary.