from what I have read mice feed on their young because they are usually lacking protein. The mothers will also feed on the young if the babies are unhealthy, or lack of water etc. There are a number of things. I use to breed mice and they really suck. I now strictly breed rats which are much easier and the odor is minimal compared to mice. I also have 7 trios of dwarf hamsters when i need smaller stuff. The hamsters have virtually no odor and start breeding again as soon as they give birth. They are very prolific, however the down side is they are very cute.