The kits will climb the cage doors in days of birth. If there is a way up they find it.
I haven't had one fall in a 36 inch cage either but I know how nerve wracking the fears can be, how we all worry.
We all do what works best for our set up, and our nerves.
I have found it's just as well to make the cage baby safe, by giving them ways to get up safely.
It's the 5-6 foot cages I worried about the most, and would take the kits and Mom out.
With lower cages now and more floor space, it's less stressful on Mom to take the Dad out.
Abby the older kits should be just fine in the bigger cage.As they are used to smaller cages I would give them play times in it first.
I think you'll be quite surprised at how well they do.