I don't even want to tell you about our last flight with ds (14 mo) without a seat....I would have paid $1000 for a seat for him if I had any idea it would be that bad! Besides the fact we could not choose our seats because we had a lap infant, when we got the the airport, the only seats left together were the seats where infants CANNOT sit!! So we had BIL, SIL, and 2 kids (one infant) together, me 4 or 5 rows back across the aisle from dd (4!), MIL 4 rows back on other side, DH 4 rows back from her on other side! It was horrible. Some kind people switched seats so DD and I could sit together. I had to pass stuff back to MIL to pass to DH when he had DS. Once he couldnt handle him squirming around and screaming, then I had to hold him....and OF COURSE the plane was about to land and took back off! That does not sit well with a fearful flyer like myself. Then DS managed to unbuckle my seatbelt with his foot and I could not buckle it, so I had to make the teenage boy next to me hold him so I could rebuckle while we had our 2nd landing! I say buy the seat, there is really nowhere for the kid to walk around anyway on an airplane, and really it is not safe. I did alot of research after the fact and clear air turbulence is the kind when flight attendants and people standing up tend to get hurt because it is out of nowhere and more severe than normal stuff. It would be very difficult to hold on to the kid during this, and they should not be playing on the ground during the flight. If they are going to be screaming and squirming in your arms for so many hours, may as well let them scream in the carseat and giv eyour arms a break.... sounds horrible I know.... I know flying is safer than driving, but there still are serious risks. Do some research while you have time. We did buy a seat for our DD years ago when she was under 2, when the flight had infant rates. It was totally worth it for us. Do what you are comfortable with and have a great trip!