But as he was offering them a ride home, his car - just metres away - rolled into the harbour.
"He just laughed ... I was shocked," said Ms Cowell.
The man had stopped after he saw the pram roll over the 2m-high wall into the water.
He turned on his car's hazard lights, then rushed to the aid of the stricken pair.
Ms Cowell said she planned to meet him to thank him for his assistance.
"He did such a good deed and then that happened to him. It is just not fair," she said.
"I wish I could afford to buy him a car."
Attempts to contact the 59-year-old man at his Harwood home last night were unsuccessful.
Senior Constable Lox Kellas, of Portobello, praised the man, who was a "good Samaritan and responded very quickly".
Unfortunately, the man had failed to apply his handbrake "in the heat of the moment".
The car was recovered yesterday afternoon.
Ms Cowell said that apart from a waterlogged cellphone and a few grazes on her daughter, the pair had escaped relatively unscathed. But they were both in shock after the incident.
"I got home and burst into tears. It was all just so bizarre."
She said that while the brake had been applied to the three-wheeled pram, that did not prevent it from tipping over, and served as a reminder to parents to be careful near water.