Our children are 2 and 5, we take:
ipod touches loaded with new games
laptop loaded with favourite dvds (our kids are fussy with TV and we often find that we cannot find anything suitable) with their headphones
snacks (homemade stuff, fruit, cheese, special stuff like natural fruit rollups and sultana packets etc...)
notepads and pens; those pens with the different colours to click down are cool
stickers
playdoh stuff called bendaroos, it's like playdoh/pipecleaners, not messy and reusable
small new toys, matchbox cars, tiny dinosaurs
That's it for the small ones.
For me I take a book, face cream, lip cream, change of clothes for all of us, some local currency to where we are going to.
And our tradition that we started with just DH and I, but have continued with the children, is that at the airport we can all choose a trashy magazine each.
Mine is fashion/gossip; I never buy these, ever, so it's a fun treat that I can pop in and out of.
Dh buys golf normally, and the children pick their own. (Tinkerbell, Thomas Tank engine etc)
We are not allowed to read these until on the plane. It takes up an hour or so so is good value. IMO.
C