In case my feelings are lost I’ll just restate I’m with kicking the kid back to Y for all the reasons listed above.
However, what I wanted to add is that remember AC doesn’t like opupping even their SEMM members unless they have to over bumping people. So AC J would tend to have more spaces than say .. UA J where it’s often filled by GS/1k or whatever pax.
AC has made it clear J is a exclusive cabin and if you want these perks either pay or use their upgrade systems - pretty much all of which also involve at least some money these days, even if it’s just booking Flex over Tango.
So why should they allow people to sit in J just because their parent/friend/whatever is there. Aren’t airlines meant to also have a manifest of where people are sitting? Can this easily be amended mid flight?
Clearly this is FT and we almost never get universal agreement