How do I get chilren of a folder oreded in this way - all folders, then all files?

It was not obvious to me how to do this. The environment I'm in is memory constrained so I can't always rely on being able to get everything and then sort it. I need to be able to use pagination as well.

So for instance, if my root folder contains these items

folder1

folder2

file1.png

file2.pdf

file3.pdf

folder3

file4.png

and I request max of 3 items, I want the children returned like this.

First call:

folder1

folder2

folder3

Second call:

file1.png

file2.pdf

file3.pdf

Third call:

file4.png

I could also solve this by being able to get just folders, and then just files (two sets of calls).

I'm using the RESTful API  (using a language that does not have higher level bindings for this.)

Thanks and please let me know if I need to provide more information.