I came back without any issue 🙂
While this Saudi Airlines page says:
If the infant reaches the age of 2 years prior to their return journey, they must pay the applicable child fare, taxes, fees and charges for that part of the journey.
In reality things are different, as long as the ticket is issued then it is ok and no one checks and the system only checks the date of the infant as of the first sector.
Credit:stackoverflow.com‘