Download much much more than you think you might need, tv shows, movies, audio books, music, games. You cant rely on wifi, so you must download it.
Chargers and back up battery/power banks. Some are banned on airlines,so check to make sure you have one that is allowed and always plug in to a wall outlet and keep the decices topped up as much as possible
run the dc before you get on the plane so they are physically exhausted before you take off
get the richard scary going on a plane picture book. It really helps to lay out what is going to happen
Bag stuff up into individual bags to keep everything organized
comfy clothes with layers for getting too hot and too cold
think twice about the 3 yr old having their own carry on as you will just have to carry it and keep track of it, fewer bags are easier
some kind of sucker sweetie for each take off and landing, and dont give it until you are zooming down the runway or they will finish it before you have taxied
dole out the snacks little by little rather than give a meal so that snacks become entertainment
be cautious about lots of fruit..can lead to loose bowels!
water bottles,yogurts, anything sealed will explode all over you when you open it after take off. Be careful you dont end up wearing it
take a fuzzy friend they can use as a pillow