I've done a long plane flight with a 18 month old & it wasn't very fun. BUT I think 3 years old is a better age too, will be easier to occupy and settle.... the younger one will be hard to keep organised. One thing is certain airlines have air host/ess focused on families & those travelling with young ones, so find out what they have available. Certain planes have individual video programs with childrens programming going constantly which can help. Activities like drawing etc are always good. I let Matilda have markers for the first time on the plane... she loved it. Snacks snacks & more snacks. And the occasional walk up & down the isle & hang out with the air hosts when they aren't serving is a great plan. I saw on some travel show recently air nannies... which go with some flights I think to Asia, but I'm not sure who or where.... sorry maybe someone else saw it?