I'll just add that if you've got a very small child in a carseat behind you and you recline your seat all the way, their legs end up about an inch from your seat back. This happened to me on the last flight I took with my 1.5-year-old son. It was impossible to stop him from making contact with the back of the seat even accidentally unless I held his feet down, which I did do, but couldn't do for every moment the entire duration of the flight. Luckily it was short-haul.

I'm completely sympathetic to how annoying it is, and believe me, as someone who's flown a lot with a baby, I am extremely active in trying not to bother the passengers around us. I know no one wants to sit near the lady with the baby. But if you happen to find yourself in a situation like the one above and you want the kicking to stop, just FYI: moving your seat up a little bit will be more effective than giving the kid dirty glances.