List of subpages in subpage blueprint

I’m trying to create this structure:

Projects
—Project 01
——Gallery 01
——Gallery 02
——Gallery 03
—Project 02
—Project 03
About
Contact

What should project.yml look like so that I can see a list in the panel where I can add and remove galleries there?

Currently I use this:

pages:
  type: pages
  label: Galerien
  template: gallery
  query: page.children

Unfortunately, it doesn’t list the galleries that already exist and there is no button for adding galleries. There is only a button for selecting pages. I was only able to limit the selectable pages to the galleries by adding the last line. I tried parent: page and some other things, but it didn’t help. I just want a normal listing of galleries in the project panel. What am I doing wrong?

Currently it looks like this, but I would like all existing galleries of the project to be displayed here.
image

I was able to figure out the problem myself. Unfortunately, the problem was not visible in my forum entry. I had mistakenly placed the blueprint excerpt mentioned under “field:” instead of under “sections:”.