There's nothing wrong with a page having no descendants. You have to stop somewhere, otherwise you'd have an infinite recursion.
I suspect what the highlighted line is trying to tell you is that there are child pages of that one, but you can't see any of them. Check with the space admins what pages are restricted.
(There's also a possible caching/queuing problem - Confluence doesn't index everything immediately. If a child page there has been deleted or moved elsewhere, and you've caught it before the index gets built for that page, it can show the "parent has child pages" > sign, but then not actually be able to list them. Give it 10 minutes and refresh the page to see if it's that)