The Saudia flight from Jeddah was said to be on its way to Kuala Lumpur, Malaysia, when the woman realised she was missing her child and alerted cabin crew.
The pilot then had to request permission to return to Jeddah from baffled air traffic controllers, Arab media reported.
The woman had left the child behind in the departure lounge at King Abdul Aziz International Airport, according to Gulf News.
A voice recording, which has been widely shared online in the Arab world, reveals how puzzled aviation staff tried to deal with the crisis.
The pilot reportedly asked them: 'May God be with us. Can we come back or what?'
One of the controllers can then be heard asking a colleague: 'This flight is requesting to come back…a passenger forgot her baby in the waiting area, the poor thing.'
They then said: 'OK, head back to the gate. This is totally a new one for us!'
The bizarre delay reportedly took place over the weekend.
Flight-tracking data showed a Saudia flight from Jeddah to Kuala Lumpur departing almost an hour late on Saturday, but it was unclear if this was the same one