How to transition fron adult coop

It may be a strange title, but my coop is a 2 level design. There is "formal" coop 2 feet above the ground, with large "room" and 4 nesting boxes. 2 feet underneath it is netted run.
We now have 3 hens hatching eggs in 4 nesting boxes, with 3 little ones 2 day old in one of them.
That "adult" chicken coop of course has a ladder that adult chicks climb no problem, but now we need to transition the little ones to somewhere they can habitate until they grow. With mama.
We are backed up by woods, fully fenced, so no larger predators, but we do have rats, can't escape that.
What will be a good suggested structure to put them in for now? Mama actually goes crazy if you try to move her with chicklets to a different place. Feeding them inside that coop, in front of nesting box, is impractical.
I have long weekend and plan on adding 4 nesting boxes to the "ground level" run. We can re-arrange mama and mamas to be into a proper structure, simply not sure what type it should be?

Thank you