In my experience you can prepare all you like but the best thing is the mantra 'It's only 12 hours' followed by another 'it's only 12 hours of my whole life' !!!!!!!!!!
Rescue remedy (for yourself)
As long as they are not doing the unmentionables - in my book lobbing things over seats, kicking seats or throwing up over innocent bye-standers (have seen all these and more) you are OK .
Apart from that from experience (I take my 2 each year on my own):
take copious amounts of food they like in the event they don't like the airline food, the airline doesn't have their kiddy meal order
if your children don't do well with sugar laden things vet the airline food - some fill the tray with nuggets, chips, lollies, chocolate and sugar laden drinks etc.....
take your own drinks especially for take off and landing helps stop ears hurting
any toys, colouring things, books you don't mind losing
if they want to watch wall to wall movies or play games I find it's easier to let them than have the tantrums
don't strap them in until its' about to tax up the runway otherwise they are over it and wanting to get out when you're about to take off
I rarely get on now at the first call for infants they get bored waiting for the plane to board, it adds another 30 mins at least in a confined space
when they bring the free wine say yes
It sounds as though you're going straight through but a 16-24 hour stop works well for us. We get off shower, find a park and stretch our legs, eat non-airline food, sleep and re-board feeling human enough to do the next 12 hours