An iPad is a lifesaver! We've done many flights with DD but the longest stretch was to Singapore, so 5 hours on the plane plus a couple of hours at the airport then another 45 minutes or so getting to our hotel. Our flight was during the middle of the day so we thought she would sleep as she normally naps for a couple of hours or so but no, she didn't sleep a wink! She went down no issues that night though, lol.

DD was almost 20 months when we flew to Singapore in April (then travelled interstate with two flights in each direction a couple of weeks later) and the iPad was brilliant for her. She loves the Wiggles so we downloaded a whole Wiggles series through iTunes and I downloaded a heap of toddler friendly apps. She loved it. We had a whole row to ourselves on the flight over plus two bassinets which was great for spreading out but DD was too big (length ways) for the bassinet. We had a bassinet on the way back but no spare seat so I wore DD in our Ergo after our meals and she happily slept for a good couple of hours, until we landed. That was an evening flight which departed around 7pm.

We've always taken our slings and used them for DD's sleep on flights (she's flown a dozen times already) and that's worked a treat. I love my Ergo now that's she bigger. The hosties won't let you wear them for take off or landing as it's against their safety regulations but I haven't had a problem using my slings during the flight (actually, on two occassions the hosties have let me leave her sleeping for landing )

As PP said, nearly all airlines will provide a meal but you must specify that you want a childs meal when you make your booking, don't assume they'll just give you one. If you book through a travel agent, most agents will do it for you. I tend to book my own travel (I'm an ex-agent) but I forgot to request a meal for DD last time and no, she didn't get one. I always take some Rafferty's Garden sachets and her favourite snacks - plus milk - so she has plenty to eat and drink anyway. I also take a selection of her favourite small toys and books which I put aside for a couple of weeks before we go so they are somewhat 'new' to her again. I bought a $5 Mrs Potato Head from Kmart to take to Singapore and DD loved it! Removing and replacing the body parts on the potato was apparently very entertaining

The suggestion of a light weight stroller is a great idea however, Changi is so well setup that you can either organise one before hand through Singapore Airlines (awesome choice BTW) or there are plenty of trollies with a toddler seat throughout the terminal. There is loads to do at Changi too so you should hopefully be able to wear the kids out before the next leg. Flying overnight for the next leg is a great plan, as is taking the kids for a swim (double check the pool is located at the terminal for Singapore Airlines though and find out if they hire towels).

Airlines are really helpful to parents with children and do their best to give you an extra seat if there is room on the flight. If you all check in together, you'll be seated together (as best possible) so you should have your entire family around you to offer extra sets of hands. Your DS wouldn't get priority over a bassinet as he'll be too big by that stage (they are reserved for the youngest babies on the flight and the weight limit is 11kg plus they aren't very roomy) so you'll most likely be seated in another part of the plane anyway.

Good luck. I'm sure you'll be fine with so much extra support around you.