It's not going to matter where the kid is seated if it is unwell and feeling miserable - F, J or Y. Sure if you pay to be seated in a premium cabin, you do expect it to be better than Y, but you are paying for the little extras, which unfortunately, does not include the right to dictate who can or cannot be seated in the same cabin as you.
Some kids are little monsters, and often the parents don't give a toss that they are kicking the seat in front, running amok etc, and others are well behaved younger travellers who are polite and no trouble at all.
Yes it most definitely is a right royal PITA when some tyke starts howling at the top of its lungs, but I've also been stuck with some utter boorish adults who should know better.
Regardless of the cabin, if you can afford to pay for the privilege, there really is nothing that can be done - (after all, if we insist on "Child-Free" zones, may I also request "Snorer-free", "BO Free", "Drunkard Free" and "Outright Tosser-Free" zones as well?
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Parents should be responsible when travelling with their children - the rest of the plane (including the cabin crew) are not there to entertain your offspring. They are yours by choice - don't palm them off onto everyone else, just because you need some sleep - because guess what, so does everyone else on the flight.
Babies cry - it's what they do and 9/10 they will drift off, but incessant seat kickers whose parents can't be bothered to reprimand them, are requested politely request to keep their kids under control. And if that doesn't work - I call an FA to request they deal with the inconsiderate oafs, which usually gets the message across.