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Mice are known for eating their young when sick, stressed, or there are too many mice in a cage. If you bother the mother mouse too much she might eat all her babies. When the babies are sick the mother tens to leave it alone to die or kill it. When you have more mice in the cage that will have or has a litter then over crowding is at hand. The mother will also eat the babies if she feels that there is no more space.
Keeping a wild animal ( not domesticated ) is not a good idea, you don't know what infection may it have and it may bite the children.