They are like mice and will breed back to back.
Mom needs foods very rich in protein. I usually feed our foster moms boiled egg, some small pieces of boiled chicken, and a wide variety of fresh veggies to help her calorie-wise. Rats are good moms and she will likely do her very best to keep the babies alive. Make sure they're temporarily in an aquarium so that there's no draft and they can't wander out of the nest and get caught in the bars.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry