as the parent of a "kicker," i can offer a different perspective. first, i customarily flew my 3-yr in his car seat, which has the distinct disadvantage of putting his feet in range of the seat back in front of him. second, the reality that all parents need to recognize is that their children will inevitably kick. i try as hard as i can to prevent it, but it never fails.

my advice, if polite entreaties to the parent(s) fail: involve a FA.

one thing that bothers me about the OP's story - why is someone flying their kid on a redeye? that seems almost borderline child abuse to me; there is no way that kid could ever get a good rest, and their schedule is going to be a wreck for the next day (if not longer).