$result1 = page('categories')->index()->findBy('uid', 'parent');
$result2 = page('categories')->index()->findBy('uid', 'child');
```
Note that this method only finds the first occurrence of a page with the given UID, which might not be the page you are looking for (if the same UID occurs several times). There's also a certain danger with using a flat structure because of that, as there is no way to make sure that the UID exists only once, so you have to be aware of this.