How should i care for a mother mouse and her babies?

You don't have to do anything but give clean water and food. She knows what to do instinctively. Just by having them in your house they will be plenty warm. You might want to give some shredded toilet paper for new bedding every so often & pull out any soiled stuff. Just try not to jostle them for a week or two. Be careful wild rodents can carry all sorts of germs especially in their fecal matter.