Answer:
At six weeks of age is the earliest you can separate babies from their mother successfully. However, if at all possible I would suggest waiting at least 8-12 weeks especially, if you are not clear on the actual age of the babies...
Actually, mice can reproduce at 4 weeks of age, so it's best to separate them at 3-4 weeks of age. If you have any doubts, if your baby mice are trying to eat solid foods, you should be able to separate them in a day or two.