The bus driver told the mother and child they had a choice: ditch the bike, or catch the bus, they say.
Not wanting to leave the bike behind, the mother and child walked from the Dunedin Botanic Garden to Pine Hill after dark on Sunday.
The bike excursion began on Sunday afternoon when Deb Friberg, a doctor at Dunedin Hospital, and her son, Judah Gray, left their Pine Hill home bound for the botanic garden.
Dr Friberg was on foot, Judah on his two-wheeler.
They planned their adventure so that when they were ready to catch a bus up the hill and home they were on a route which ran bike-friendly buses - those with bike racks fixed to the front.
But when the bus turned up, the trouble began.
The bike was too small for the bus' bike rack, which couldn't lock shut, Dr Friberg said.
She suggested they be allowed to take the bike on board, but even though the bus was empty, the driver said no.
Dr Friberg argued the bike was no bigger than a pram, and pointed out the absence of other passengers.
But the driver gave her an ultimatum, she said.
''He said you can either decide to leave the bike here or you can get on the bus.
''He was quite curt. He was `no we're not having the discussion and those are the rules and that's the law'. He was quite cold.''
Dr Friberg's husband and Judah's father, Abe Gray, said yesterday the incident had upset their son.
''The bus driver was curt, and left them very stranded with a crying child, which wasn't a good experience for [Judah].
''He [the bus driver] just shut the door on them and drove away.''
Mr Gray said the incident highlighted a problem with the city's bike and bus services.
''Either someone's being very impolite or there's a major gap in the services being provided.''
Otago Regional Council support services manager Gerard Collings said bus operators would ''generally say no'' to allowing bikes of any sort inside a bus ''on the basis that the bikes aren't able to be restrained''.
The same rule meant other bulky items, like surfboards, were also not allowed on buses.
''The reality is, defining whether something is secure or not is a driver and operator call.''
Prams could generally be folded up, and buses had special spaces set aside where wheelchairs could be safely parked, he said.
Mr Collings confirmed buses' front-mounted bike racks were designed for adult-sized bikes, leaving no provision for bus travel for people with small bikes.
While there were no plans to change that, the ORC was always listening to feedback and discussing that feedback with operators, he said.
Go Bus Otago Southland regional manager Ben Barlow said the bus in question was operated by Go Bus.
''It is unfortunate the bike didn't fit on the rack. But we don't allow bikes of any size [inside the bus].''
He said the bike racks fitted were a standard size across New Zealand.
All customer feedback was important and was investigated, Mr Barlow said, and the company demanded high levels of service from its staff.
''If the driver hasn't adhered to that, we will be talking to him.''
