It looks like Martin's Cages is back up and running (they were shut down for a while). All their cages are collapsible, though it can be a bit labour-intensive to do so (you have to remove all the metal rings or zip-ties that hold it together). I used to have one of their huge cages years ago for my rats and I loved it. Very sturdy and well-made, and reasonably priced. Only downside is that the platforms are all wire mesh (though the mesh is correctly gridded for safety, at least) and the pans are plastic, but some fleece covers would help with that (so long as your kids aren't fleece chewers). Here are all their chinchilla cages. As you can see, you have quite a selection of sizes to choose from, so you can select whatever you feel best suits your needs:
Chinchilla Cages | Martin's Cages
I also found this, though I'm not sure it's big enough, especially for two. It also has a wire floor, but you could remove it and cover the plastic pan with fleece:
Wayfair.com - Online Home Store for Furniture, Decor, Outdoors & More
I think a Martin's cage would probably be your best bet, honestly. Martin's are likely to be way better quality than anything else you could find for the price (at least, that was the case a decade ago when I bought mine). They're not pretty or flashy, but they're sturdy and functional. My only complaint about them is that their designs are not the easiest to clean....and the larger the cage, the truer that is. But many now come with the option to have a flip-top that opens (mine didn't have that feature), which probably helps.
