Don't get uptight over little things. Flight delays can be really annoying, but stressing about setbacks only makes them worse. There's nothing in the world you can do about them, so instead of thinking your hol is off to a bad start already, think positive: take the time to chill out in Departures, and why not buy or borrow a Greek phrasebook and learn a few handy essentials?!
Think positive
If, instead of blazing sunshine, you end up with pouring rain for 13 days of your holiday, use your imagination. There are still loads of other things you can do: board games, walks in the rain followed by cakes and treats, funny photoshoots with the family, etc etc. Turn unfortunate weather into an opportunity for maximum fun and everyone else will too - especially kids, who naturally invent spontaneous fun.