I can't help you with the ebook/flying question, but I can try to help with the kids and flying question
I get carsick myself if I'm a passenger, but I've never been sick in a plane, never even felt slightly motion sick. For me it's about the images flying past the window and you just don't get the with a plane. I doubt colouring would be a bad idea for the kids, in fact, it's possiblel the airline will supply the kids with a colouring/entertainment pack. You can get headphone adapters that let you contect two sets of headphones into one headphone jack, that might make it easier for them to watch movies on the netbook. Do they have portable game consoles like the DS, that would keep them entertained for the flight.
You can get motion sickness meds from the doctor if you're worried about it. I tend to avoid them, though.
Good luck!