To prevent the seat kicking with the littler ones, we found that the CARES seatbelt that sittin pretty recommended to be great, since the child is sitting in the big seat and can't reach the one in front. http://www.kidsflysafe.com/

When DS got a bit older, just explaining to him how uncomfortable he's making the person in front of him seemed to work. Well, that and withholding candy... smile