I used to breed my own mice and rats and eventually gave up. The mice would breed fine, but they'd turn cannibalistic and eat the babies. I had them in a 40breeder tank, they were healthy and clean, and they still killed the babies.
Sometimes you can fix whatever is causing them to be that way and sometimes it just happens and you can't do anything about it. some are bad mothers, bad breeding mice.

Good luck with it though.