Oh, I have done this so OFTEN.
Whatever you think of as stocking-type presents; take one for every hour of the flight, less five hours. Colouring books, set of six crayons; our great saviour was Playmobil kits, the tiniest ones. A picture book with things to find, of the Where's Wally sort. Stories to read. Puzzles and mazes for the five-year-olds.
Frankly, they need your attention most of the time, and when they go to sleep, it's on you. You will arrive a bit limp...
Ask the airline about milk. My bet is that they don't provide it. They don't provide much except adult drinks.
DON'T go for the bulkhead seats unless the airliner only has back-of-seat screens, or your dcs will be kept awake by the pulsating screen above. They are also always near the loos and people come and go all night.
They are also near other families who may be less well prepared and whose children may make some noise. We were on an intercontinental once with a family of 3 kids where Mum had brought NOTHING to entertain them. Dad curled up and went to sleep, leaving her to 'cope'. (That said, the passengers I tend to hate are the childless ones who wet their pants laughing at the comedy entz, at 2am....)
Phenergan is brilliant as a knockout drop. Tell the chemist ds or dd has trouble sleeping due to exzcema (sp?). It would stun a healthy horse. Also brill for jetlag later. Usually makes them slightly cranky next day, but worth it to get through the lfight. DS slept from LA to Sydney (14 hours) due to its magic. Dd took it less well.
Be careful about food. Take some packets of something simple like raisins. Dd was spectacularly sick flying in to Kingsford Smith, in dh's hands... too much airline chocolate.
Go with God!