Conditional styling of wp_list_pages bullet points

I’m looking for some type of script that allows me to select custom image bullets for my wp_list_pages for 3 scenarios:

1. If a page does not have a child
2. If there are children
3. If a page was recently updated, provided that the page has children

I’m not sure how to do this. Since the depth of the children can vary, I would not edit style.css for for my last child.

Since the wp_list_pages is what outputs the ul, I’m not sure how to write an argument (perhaps in my Walker class) that says if this page has zero children, .

Can anyone advice on this?