The mother probably ate them cause she felt that it was not safe for them, maybe something was wrong with them, or the most common thing I have seen with mice and rats, she is a rogue, and usually when they eat thier babies once, they WILL eat any other litter they will have after that. So, you got a decision to make, either try and breed her again and see if it happens again, or feed her off to your snake/snakes and get another female to breed with. Also, I reccommend if you are breeding to get feeders, you should have a breeding group of 1 male to at least 2 females minimum, but 3 is great. And dont keep around any rogues, for some reason, they can get your other females doing that... hope this helps.