We have travel w/my now 3 & 6 yr olds on flights & some long ones since they were born. The last flight was 3 weeks ago for a total of 12 hours. A couple of suggestions--- 1) if possible upgrade to 1st the more room the better 2) redeyes work well, make sure you have lots of activity during the day and no naps, they sleep on the plane all night 3) Get a bunch of activity books w/stickers that u're child has interests in(barbie, dora the explorer, etc.) and surprise her w/them on the flight, spend a lot of time doing them slow and reading and it turns into real learning as well as quality time 4) Let them talk to the flight attendants and make friends 5) a small favorite toy that has gotten misplaced into your carry on, for the 2 weeks prior to the trip and then suddenly appears w/some new accessory is always good for another 10 minutes or so.
Enjoy best of luck