Reddit mentions of ClosetMaid 6222 Hanging Basket for Wire Shelving

Best thing I could find (10.7 x 18.4 x 8)

The only thing I would worry about is the little ones chewing on the coating, this size should cover 1/3 long ways.

Also you may be able to use the hooks on this not only as a stand but you could make very small holes and hook it to add even more room.

However if this doesn't work, you could add adhesive hooks so you can use cage hooking items like this

If the hooks aren't what you want then you can add items like these:

Best Option

Wooden Balcony

Platform

Platform and Swing

Platform and Swing - The Squeequel

I really hope this will help you and the little ones out!

Edit: Forgot to add this one

These ClosetMaid shelves would be perfect for your space!

They have little hooks that hook onto the shelf that’s at the top of the closet (they’re flexible so they can hook onto the bars even if they’re an odd width apart), and then they can also hook onto each other.

We currently have four of them hanging from the top wire shelf in our closet (one from the shelf itself, then three more extending down below that), and they’re great for open-front storage that’s easy to see and access. Ours our being used for clothes right now. I have them set up so that the side walls are vertical and not on an angle, but you’ve got options.

Just roughly eyeballing your space from the picture, it looks like you should be able to fit two rows of the hanging shelves side by side, if you wanted to (they’re 17” wide).

I’ve taken the ones I’ve got with me through the last four moves; most places have some type of wire shelving, so they’d be useful beyond just your current apartment. They can take a lot of weight (in one place I had them stacked four deep holding bottles of liquids, and they didn’t bend or break at all), and they nest neatly inside each other in a standard size moving box when it’s time to move.

There’s also a link on the Home Depot page to a similar type of hanging shelf that’s 24” wide, but it looks like it doesn’t have real side walls/a back wall. The ones I linked that we use are like baskets, so they’d be great for the papers/books/binders/office supplies you mentioned.

ETA: Looks like they’re a little more than $3 cheaper per piece on Amazon. The fourth picture on the Amazon listing is how we have ours set up, only with additional baskets below it.