well I feed that forti diet or what ever its called too.
As mention in a previous post you need to provide high quality diet, food found in pet store are not high quality diet, I would recommend Mazuri 6 F or harlan mixed with some dog food. (without the red dye)
Today I saw two more babies killed its about the 6th day I dont know if me putting my hands in the nest is a bad thing or not??
As explained previously as well the lower the stress the better with mice.

Breeding mice is not that hard one you have an established colony, the hardest part is to get started and again diet an low stress are VERY important with mice.

I have bred mice for several years now and have zero case of mothers killing their youngs, the firt litters are always perfect, the only time a baby will be eaten is when it simply does not make it.