A mis-spelled christian name they shouldn't be woried about, particularly as you have notified all parties (and they have changed the name in the booking) as well as having his passport there as confirmation. They would be much more concerned if your son's surname was mis-spelled as it would not match up with passport details.

If you are really adamant that you want to fix the problem, the only way is to get it re-issued but I'm not sure what Qantas office you'd find over there. You have enough time if you can find an office.

Hey, regardless, enjoy the flight!!! I had the pleasure August 02, something I'll never forget.