I agree with suggestions and we went through some of those activities but they are probably more practical on 2-3 hr flights. This is 12-15 hr here - perhaps i am just not creative enough...
I do prefer having tired kids on arrival than well rested - never had any problems with tantrums - they would just drop asleep at hotel and we all get nice rest. On a couple occasions they were wide awake after sleeping in flight while we were dead tired and it was quite miserable.
Again ymmv - i only comment based on my experience.