Hi,
This very much depends on who you are flying with, if you have on flight enetertainment, it helps, my kids are 8n6 and have been goin since they were 3n5, and I have never had a problem. Virgin have a kids channel and films that keep them occupied for a good portion of the flight, the novelty of the headsets and tvs are enough for starters.
The food and drinks keep them distracted as well with the main meal, drinks, snacks, ice cream etc time does pass quite quickly.
Take off and landing obviously is interesting for them, especially landing as you seem to go low for quite awhile and the views are amazing, mine play 'spot Disney' (they never have done yet!!)
I think this leaves about 3 hours for potential "I'm bored" time,
Virgins backpack is good but I also fill a bag with the usual stuff, crayons, travel games etc.
Woolworths are very good as they usual have a section with travel stuff, I got some little packs filled with loads of stuff that were good value. All of the stuff I pack I keep a surprise so when the time comes I can reveal stuff to keep them interested.
I also get them to write lists of things they want to do, and starta diary (this never lasts but it will while away 1/2 an hour.
In case of grizzley headachey kids, that are probably just over tired, I pack Medised which is a strong Calpol, and has been a life saver when they were smaller. To be honest, they are brilliant now, and as they know the drill they just get on with it and dont moan too much and amuse themselves!
Hope this helps
Have a good one!