When our two were young babies they were ace on planes apart from one time when the people behind thought it fun to tease one of the kids so it got her excited - and thus - then sick.
Take lots of things for them to do - try to get them absolutely worn out before they get on the plane and yes - they tend to love looking out of the windows.
Ackshully for our kids most of their first flights were in business class (perk of the then job) & when the little lad had his first economy class flight he asked 'Where's the big seat?'
Spoilt lil' bugger!
(and yeah - don't let 'em kick or pull on the seats - it is f(airly) annoying).