I was thinking it would be nice to have the links to Child documents automatically show up at the bottom of the parent document. This way you could easily jump to the next document.
The same would be true in reverse. So from the Child Document you could link back to the Parent Document. It might make sense to put the link back to the Parent in the header area rather than footer, or possibly include in both locations.
Another option, and how for example Gitbook does it, would be to have "prev/next" links at the end of the document so that you can go through your documentation page at the time.
Showing child documents below the parent document will be pretty useful, as we are using parents to make categories of children. But the parent page itself is empty.
Similarly, children can have breadcrumbs on top to go to the parent.
Same here, we're using parent pages as category containers, it would be very nice to add an index instead of "recently edited"
Update: Now added a breadcrumb at the top of the document that points to the parent(s), looks something like:

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Update: Now added a breadcrumb at the top of the document that points to the parent(s), looks something like: