In Reply to: You can buy... posted by melbmeg on Tuesday, 23. August 2011 at 16:07 Bali Time:
best bet and I don't really see the need to take a carseat. When my very active daughter was a bit younger (and even now she's 5) we chose flights at a time of day when she would be likely to sleep some of the way (eg, lunchtime flight when she was still having an afternoon nap and now a flight leaving at 6.45pm coming home as I know she'll sleep most of the way). We never had any spare seats available between us, she just slept laying across both me & my husband.
I will probably be flamed for admitting this, but we have also been known to give her a dose of antihistimine to be sure she would sleep (on our first few overseas / interstate flights). If you do decide to go that route, you need to test on your child beforehand as sometimes it has the opposite effect to the desired sleepy state!