That's funny, I want to do the opposite thing. I want to show all child pages of a certain page (like I could do with Multi Pages widget), WITHOUT having to go and tell it specifically to include those pages. Whenever I make a new page, it does NOT appear for me automatically. So what I have going on is what you want, and what seem to have is what I want.
To that end let me tell you what my settings are:
using include, selecting the parent page, and clicking show subpages, does not work for me; all I see is the parent page. So I have to use include and highlight ALL that pages I want to appear.
Now, tell me how yours is set up, because I want what you have!