Food has a LOT to do with cannibalism, and litter size. If the mother isn't properly fed, then she can re-absorb, or abort fetuses that would have normally (on a good diet) been born.

If the mother births, and is feeling low on any important nutrients, then she may also eat her babies to fulfill needs that her body is telling her are low.

Stress is another factor that can cause cannibalism (food related, is one type of stress), from too many ASFs in a small space, from not liking one of it's cage mates, from not liking the litter, or even not liking the smell of a candle you're burning. LOL!

It's probably something simple like feed though, and nothing finicky like a candle.