regarding workarounds, i’ve seen folks create projects for each place and then group the projects in an umbrella project. this eliminates the need for a parent place, though that method comes with pros and cons.
i’m not aware of a great way for normal users to identify child places. the old API (see https://www.inaturalist.org/pages/api+reference) allows query for places filtering by ancestor places, which might get you the desired result in your case, though i believe there’s not a good way to limit the results generally to immediate children. the other problem is that the old API is deprecated and could be retired at any time.
the final workaround might be to use the list of all places that they recently made available. (see https://forum.inaturalist.org/t/use-wikidata-for-place-names-and-wikipedia-descriptions/7702/13 .) that list includes an ancestry field, which you could parse to find immediate children relatively easily.