There were 2 issues:
- YAML is indentation-sensitive, so descendants need indentation
- You can't mix object keys with array elements eg:
```yml
- one:
title: Title
- Invalid
```
So if you want to nest, then you can't use the shorthand:
```yml
- file/folder: Pretty name
```
You have to use:
```
- file/folder:
title: Pretty name
children:
- document.md: A document
```
