I flew a 10 hour flight with a 7 week old (oh, and the week before sat on a plane for 6 hours with a 6 week old, which didn't fly...) at Christmas. It was completely fine. He was too tiny to need entertaining, just slept or breastfed, and even when he cried he was so tiddy that no-one could really hear him. The staff at the airport and on the flight were incredibly nice to us, cooing over him and helping us out at every turn. On the way home, the night flight, he slept for quite a lot of it so we could too. Our 3 year old was very good for his age, but he was much harder work than the baby! One thing to be wary of though is that a holiday with a tiny baby is not a holiday in any real sense of the word - you'll want to be doing lots of things, seeing lots of people, socialising... and you'll hardly be sleeping. We had a lovely time, but it's good to be prepared to feel a bit knocked out. If you have kind family around to look after the baby while you have a snooze that will really help.