Trying To List Children of a Post using Show Posts

I was finally able to get it to work with the filter. Not sure what was wrong. Any chance show posts can be updated so it allows the query args to pass through?

Which query args?

For example in this case apparently it's not possible to pass post_parent in the query args. I was passing it in but somehow it was being ignored or removed. It would be great if show posts could accommodate the same arguments that get passed to get_posts. That seems easy but I haven't looked at the plugin code.