Here's what I do.
When 20 days have past, I start checking for chicks by peaking under the hen. (Warning, some hens bite - and yes it can hurt!) Once I see chicks, I put a baby chick waterer and food near the momma hen for the babies to reach it.
After a day or two I move the hen and her babies to a large dog crate. I find it works out well to put the babies in a bucket, and hold the momma upside down so that she can see her babies while I carry them to the new pen. I use the dog crate, because some kitty cats don't see cute little fuzzy butts, they see chicken mcnuggets with feet.
You can add extra chicks while she's still broddy on the nest. If she's only hatched out 2 chicks, you can go to the feedstore and give her whatever breed that you want. I also grab any extra eggs on the nest and put them in the incubator. That way if a chick needs and extra day or two, then he/she has the chance. Plus, sometimes another hen will lay in the box after the hen has started to brood. (Sometimes the mother hen will try to stay on the nest to hatch out all the eggs, so the earlier ones can actually starve to death.)
Once the chickens are in the dog crate, I provide them with the baby chick food and waterers in the baby chick feeders and waterers. ) Baby chicks will drown if you leave them anywhere near a bucket of water!!! Use the baby chick ones, or a few empty cat food cans - with a few rocks)
Once the chicks are a week old, then I move the momma and babies to a larger pen. One of the pens that I'm using now is an old camper for a truck that I no-longer have. It has windows for lights, screens for air, a door to open and close, and an open bottom for grass. That way I can move it every few days for the chickens, chicks to get new grass. It's unconventional, but it works. The chickens and their chicks are all happy and safe from 4 legged evil ones.
There is no perfect approach, just find one that works for you and keeps your babies safe. Remember, some cats are evil, ( other's are okay, I have a few that like to sleep near the day old chicks with no problems, other's that love the fresh mcnuggets), chicks need chick food, momma hens are very protective and will bite, chicks need chick waterers, and baby chicks are adorable. Hope this helps.