Do you have any pictures of what it looks like? Or something like it on the internet?
If you are going to be using a cage that has no levels in it, you can always make your own levels! I do that with my cages. I buy a corner shelf, but something on top of it so their little feet can walk on it, and I use zip-ties to hold it in a corner. It works great!
i had the superpet extra large for awhile (purple bottom, right?) only problem with it was my girls could escape through the bars. i put wire and zip ties all over it, and it worked, but it looked terrible.
hopefully your kids will be able to stay in just fine!
If you have any doubts about the size of your cage, you can put the dimensions into a cage calculator to find out if it's big enough. There is a sticky with links to cage calculators at the top of the rat homes forum.
You know, I actually think it's sad that the company calls that their extra large cage. I mean, it's perfect for rats, and a really decent cage for rabbits and guinea pigs, but the fact that they have to call it extra large because they sell so many smaller cages (that are considered 'properly sized') is just wrong. I think it should be their 'medium' cage and they should discontinue their small ones.
Anyways, you might just consider just adding your own levels and always keeping them in that cage, since it really can provide a lot of room if you use the space properly.