Not exactly on the topic of kids kicking the seat but similar.
A long time ago, when i was flying MDW-DEN on an ATA 738 is what I believe it was, there was some buisness man sitting behind me. I had a window seat in row 6 or 7 (or something more upfront!) Anyway, he managed somehow, a way to stick his smelly right foot betwen the wall and the seat and place it on the right hand arm-rest. There were no shoes, just smelly socks. I asked him two or three times, and by the third time he told me to shut up, its only a 3 hour flight, and that he did lots of flying before, and he was tired. (Like I care?) Anyhow, I got so irritated, that I lifted the armrest, it was liftable if thats what your asking, and slammed it down on his foot, not very hard, but hard enough for him to move it away. I guess he kind of liked it to a point, since he had the urge the stick his foot a couple of more times, which prompted a few more slammings, but after this 15 minute battle, the "territory" was reclaimed by me!