"is North America overpopulated?"
There's an abstract sense of overpopulated (sometimes described as turn all of texas into Manhattan and abandon the rest of the planet and texas would still only be half full)
And then there's carrying capacity sense of overpopulated. Both food, and west of the Mississippi, water, is actually the limiting reagent (Los Vegas will be simply out of water in a generation or so...). There's already a cultural impedance bump when westerners talk to easterners WRT water "waste".
Mexico is tremendously overpopulated from a carrying capacity standpoint. Canada is in pretty good shape. USA in between.
Do those parents and grandparents really support their grandchildren or they only want them happen and then do nothing about it?
Anyway, children living near a large city are more capable than ever of giving them the finger, and that's what they going to do. See in the concurrent thread, "If they decide to have children" - meaning your default is to not have children.
World may be overpopulated, but is North America overpopulated? I guess it actually isn't. Most of places outside South Asia aren't overpopulated. Having some population growth and economy growth and no fears that social security would implode is better than having decline and being in panic like Japan does.