I flew with my wife and younger daughter last October from LIS
. Our girl was a bit older than your infant ( 23 months old...) but she behaved really well, one thing we tried was to keep her sleep schedule has much has normal, if you are travelling to Australia it's going to be like 8/9/10 hours ahead, we found that in our trip ( and because it was the oposite way, 8 hours behind ) keeping our girl having her portuguese schedule sleep time really helped us great. First flight from LIS
, no problem, then from AMS
she actually slept almost all the trip, around 7 hours, so that kept her well rested. Then when we arrived to FAT
she quickly got California schedule and all went well. On the way back it worked fine too, this time we did FAT
, she did really well all over until we crossed USA, then when we arrived at PHL
she started to sleep and she did that almost until we arrived to LIS
. I don't know about your baby, but normally airlines like Virgin will have good stuff for kids, they will play a bit, the food will be ok, maybe you should check out if your are allowed to bring your kid favourite food too, sometimes they don't accept too well airlines food so any special things he likes it's always good, plenty of water, and pay atention to some passengers.....there are some really "pain in the ass" people travelling!!! In our first flight from LIS
a lady just before we took-off "advised" my wife to control my kid....of course I didn't liked that and I said that she was a baby and if she was not happy flying Economy Class then she should move or get "upgraded" to Business!!! You can find really very, very stupid people around that maybe never had babies before or they forgot that!!! But simply you and your wife stress your points, of course you'll do your best to keep the flight calm for the rest of the people but please don't get overhelmed if you baby have some problems!!!
Regards and a great trip to Australia!