It's not okay, and you of course try to stop it. That's a given, and part of the reason why I don't need the aggrieved traveler's input on the matter during the flight. But a child's feet in a carseat are going to bump the seat in front of them from time to time, because that's where they hang. If he's straight-up kicking it, I'd remove him to calm him down and tell him that's not okay. But if he's bumping it unintentionally, no more than periodically, and you turn around and pop off after the third contact, as you claimed you would earlier, that chat isn't going to go well for you if you're impolite.
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