This is a special post for quick takes by Cleo Nardo. Only they can create top-level comments. Comments here also appear on the Quick Takes page and All Posts page.
I don't think it's clear on longtermist grounds. Some possibilities:
If you think that the amount of resources used on mundane human welfare post-singualarity is constant, then adding the Zambian child to the population leads to a slight decrease in the lifespan of the rest of the population, so it's zero-sum.
If you think that the amount of resources scales with population, then the child takes resources from the pool of resources which will be spent on stuff that isn't mundane human welfare, so it might reduce the amount of Hedonium (if you care about that).
If you think that the lightcone will basically be spent on the CEV of the humans that exist around the singularity, you might worry that the marginal child's vote will make the CEV worse.
(I'm not sure what my bottom line view is.)
In general, I worry that we're basically clueless about the long-run consequences of most neartermist interventions.