Years ago, on a CX flight from JFK-HKG in Y, a little kid, maybe 5 years old, was kicking the back of my brother's seat. Like, kick kick kick kick, constantly. Because he was bored. My brother kindly asked the mom to get her son to stop, and she nodded. But it continued. He asked her again, but it still continued.
Finally, he called the FA over, and said to her, loud enough so the mom could hear, "This kid is out of control and kicking my seat. Do you have, I don't know, a cage you could put him in?"