Yes, my active 3-year old kicked the heck out of the seat in front of her all the way from Chicago to LA the last time she was in a car seat on an airplane. The car seat gave her the extra few inches so her little legs could reach the seat. I felt horrible, but there was nothing I could do about it once she was in the seat as there was no place else for the car seat. She flew strapped in with the lap belt on the way back.
For the comfort of the people ahead of you, I would recommend that you bring the car seats as luggage and use the lap belts instead. Bring lots of toys/games/coloring books/etc to keep the kids happy. Make it clear that they cannot remove the seat belts (yes, I know ... easier said than done).
Good luck!
I use a car seat on an airplane for my children for safety. Yes there are other bonuses such as them feeling comfy and falling asleep

but the primary reason is their safety. They do not fit into the seat belt and would not sit in it w/o putting themselves out of position and placing them at risk in a dangerous situation.
Because my primary reason for using the car seat is safety that means that MY child's safety comes before other passenger's comfort.
Yes, I will do everything I can to make sure that my child doesn't kick their seat but if it happens...I'm sorry but I'm not putting my kids car seat in w/ the luggage.
Oh, and FWIW, my children always fly w/ carseats even when under 2yo. We also use them rear facing until they outgrow their seat (generally between 2 and 3yo). My ds will be turning 2yo while we are at WDW in December and will be rearfacing both ways on the plane. I rear face him for safety reasons, but the bonus is that he can't kick the seat of the person in front of him!
To the OP, Check out this
link for more information about using your car seats on an airplane. Pay special attention to the part towards the bottom that explains about flipping the buckle on the airplane's seat belt so it makes it easier to release when you are getting off the plane!
If you have any questions, just give me a yell. I'm a Certified Child Passenger Safety Technician and even though 99% of our training is for usage in cars, I have some resources for airline use as well.
Good Luck!