I had that cannibalism problem when I first started breeding mice. I analyzed possible causes by figuring out the make up of the animals being eaten, amount of food kept available and variety of same.

As a result of my analyse, I added, weiners to the diet (any left over meat product: chicken, beef, etc_) to supply fat product to the diet, corn on the cob, cat food (not much dog food anymore) Apples..etc. and of course the Rodent chow.

They also get the sun lamp shined on them thoughout the week.

The variety of food available and the addition of fat to the diet and FULL food trays seems to have resolved the issue.