If the babies are cold, you can warm the nest by placing one of those cloth rice bags you nuke in the microwave under the box. Or wrap a kitchen towel around a heated rice bag, then place some fur and babies on top of it. REMEMBER that the babies can get quickly overheated so don’t put them directly on the rice bag. While the warmth may feel good to you, it is way, way too hot for newborn kits. It can harm the hairless, thin skinned babies. I remove the box to do this and continually check for overheating. They cannot regulate their body temps or even move away if they get too hot. You can use a regular heating pad under the box or a hot water bottle inside it.
After the doe kindles, give her a treat to eat away from the box so you can remove and examine the babies. Now is the time to clean up any blood, afterbirth or dead babies. Do a head count and write it on the cage tag with the actual delivery date. Make note of how many normal size and how many peanut babies on her cage tag. Peanuts are kits born with the fatal double dwarf gene. They are much smaller than normal kits and normally expire within a few days. You’ll need to remove the peanuts when they expire.