Ottawa's transit union is defending a bus driver who drove away with a toddler on board after leaving the little girl's mother at the curb during a dispute.

Andre Cornellier, head of the Amalgamated Transit Union, said he can't understand how the child got on the bus without her mother.

"Why wouldn't that mother keep that child beside her?" he asked Tuesday. "There was a time when people would keep their kids very close to them … But now parents let kids go all over the place."

He added that bus drivers have no way of knowing which children belong to which passengers.

A statement issued Tuesday by the union said the incident was an "example of the operator's concern for passenger comfort and safety being misunderstood."

The incident took place Saturday evening when Sarah Pacey, 24, was trying to board with her two-year-old daughter Aimee and a stroller carrying her seven-month-old baby Lea-Marie.

Pacey and the driver got into an argument about whether the stroller should be allowed on board, as another passenger had already boarded with a stroller. The union alleges that because the bus involved was an older model with a narrow aisle, the operator thought allowing two strollers on board would block it, stopping other passengers from getting on or off.

The driver allegedly drove away with Aimee on board, but another passenger chased the bus, and the driver let the child off about 100 metres away.

Driver 'deeply sorry': union

The driver was subsequently pulled from duty and sent for retraining pending the results of an investigation.

According to the union, the driver didn't know the child was on board, stopped immediately once he was aware of that and is "deeply sorry for any distress he unintentionally caused."

OC Transpo said Monday that there were few passengers on board at the time, and safety did not appear to be an issue. The city-owned public transit company currently does not have a policy on strollers.