We flew Sydney to London return at Xmas (plus 3 hr drive to airport & back on Sydney side) when DS was 7 months and then one-way to London in July at 14 months.

Our DS is not great at going to sleep but he got tired & slept well on the plane. As Sammijane suggested an extra seat is great (bassinett is good if baby is small enough) but take some dark fabric to drape across seats to keep lights off your sleeping baby. We suspended some black fabric from back of our seat to inside of tray on seat in front - this really helped DS to sleep longer.

Dont worry too much about other passengers - they are usually plugged into the entertainment system so wont be bothered with baby noises.

We ran up & down the isles with our mobile baby & made loads of friends....everyone loves babies!!! Lots of people on the plane will have been in our position at one point in time & will be very understanding.

We found the biggest problem wasn't DS getting sleep but us. I'm not sure how to address this one but a big sleep when you arrive will help.

Have a great holiday & Happy Birthday to DD!!