His son walked more than 6km from The Plaza in Whangaparaoa to the family home in the strong winds of last Tuesday's stormy weather.
The father, who did not want to be named, said his son became sick as a result, and the Hop card had been wrongly blocked even though the account was at $20.28.
Auckland Tramways Union president Gary Froggatt said such incidents were happening frequently.
Mr Froggatt, whose union represents 890 bus drivers on routes from Orewa to Pukekohe, said all passengers in similar circumstances should stay on the bus.
"Tell the bus driver to call a supervisor and refuse to get off. Bus drivers do not have authority to refuse travel, especially [to] children, without consulting their company unless the situation involves personal safety or the protection of other passengers," Mr Froggatt said.
An Auckland Transport spokesman said that without more information, such as the Hop card number, it was impossible to follow up with the bus company involved to determine what had happened.
There were a range of possible explanations. The network carried more than 175,000 bus passengers every week day, he said.
"In cases of genuine error or where there may be safety concerns - for example, a young child travelling alone - we expect our bus operators and their drivers to show a level of discretion and initiative."
Mr Froggatt said since the new AT Hop system was brought in such incidents had increased noticeably.
"Sometimes it's the passenger's fault because they haven't loaded sufficient funds [onto their card], other times it's a fault of the bus."
