Remember that guys when you accidentally kick the seat in front of you and someone turns around and clocks you.

And yes, I've done it and it's happened to me too.
Accidents happen. Apologize, fix it, and move on. Apparently, depending who you believe, if it didn't happen repeatedly and the woman did this, there's no excuse for assaulting a kid. If it happened repeatedly, the pax should speak to the parent and not to the kid.
I've dealt with more bratty, entitled adult pax than I have bratty kids on planes.
Apparently everyone forgets what it was like to be a kid.

A lot of kids don't realize it and "controlling" a kid is easier said than done. Say something to the parent if you must - go for it. But the entitled and bratty attitude is found in adults much more often.